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 $214.61   8.661%   $233.1974   $233.20   $233.20   $233.20  
  Purchase #2 $50.92   7.347%   $54.6611   $54.66   $54.65   $54.70  
  Purchase #3 $242.94   10.286%   $267.9288   $267.93   $267.95   $267.90  
  Purchase #4 $177.88   8.566%   $193.1172   $193.12   $193.10   $193.10  
  Purchase #5 $119.61   13.399%   $135.6365   $135.64   $135.65   $135.60  
  Purchase #6 $31.74   5.692%   $33.5466   $33.55   $33.55   $33.50  
  Purchase #7 $117.77   13.430%   $133.5865   $133.59   $133.60   $133.60  
  7 purchase totals = $955.47       $1,051.6741   $1,051.69   $1,051.70   $1,051.60