Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $249.87   7.122%   $267.6657   $267.67   $267.65   $267.70  
  Purchase #2 $137.74   11.573%   $153.6807   $153.68   $153.70   $153.70  
  Purchase #3 $146.70   12.641%   $165.2443   $165.24   $165.25   $165.20  
  Purchase #4 $183.39   5.811%   $194.0468   $194.05   $194.05   $194.00  
  Purchase #5 $184.61   6.642%   $196.8718   $196.87   $196.85   $196.90  
  Purchase #6 $188.68   10.800%   $209.0574   $209.06   $209.05   $209.10  
  Purchase #7 $162.31   7.306%   $174.1684   $174.17   $174.15   $174.20  
  7 purchase totals = $1,253.30       $1,360.7351   $1,360.74   $1,360.70   $1,360.80