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 $187.72   3.463%   $194.2207   $194.22   $194.20   $194.20  
  Purchase #2 $60.44   8.278%   $65.4432   $65.44   $65.45   $65.40  
  Purchase #3 $78.40   4.824%   $82.182   $82.18   $82.20   $82.20  
  Purchase #4 $108.54   12.215%   $121.7982   $121.80   $121.80   $121.80  
  Purchase #5 $188.64   11.561%   $210.4487   $210.45   $210.45   $210.40  
  Purchase #6 $245.53   9.586%   $269.0665   $269.07   $269.05   $269.10  
  Purchase #7 $68.79   8.541%   $74.6654   $74.67   $74.65   $74.70  
  7 purchase totals = $938.06       $1,017.8247   $1,017.83   $1,017.80   $1,017.80