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 $224.26   13.423%   $254.3624   $254.36   $254.35   $254.40  
  Purchase #2 $235.53   4.665%   $246.5175   $246.52   $246.50   $246.50  
  Purchase #3 $218.31   6.298%   $232.0592   $232.06   $232.05   $232.10  
  Purchase #4 $248.37   7.664%   $267.4051   $267.41   $267.40   $267.40  
  Purchase #5 $7.65   4.744%   $8.0129   $8.01   $8.00   $8.00  
  Purchase #6 $84.86   10.742%   $93.9757   $93.98   $94.00   $94.00  
  Purchase #7 $97.71   6.692%   $104.2488   $104.25   $104.25   $104.20  
  7 purchase totals = $1,116.69       $1,206.5816   $1,206.59   $1,206.55   $1,206.60