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 $225.73   6.770%   $241.0119   $241.01   $241.00   $241.00  
  Purchase #2 $104.72   8.631%   $113.7584   $113.76   $113.75   $113.80  
  Purchase #3 $249.25   13.615%   $283.1854   $283.19   $283.20   $283.20  
  Purchase #4 $57.28   4.387%   $59.7929   $59.79   $59.80   $59.80  
  Purchase #5 $97.29   11.234%   $108.2196   $108.22   $108.20   $108.20  
  Purchase #6 $137.75   4.183%   $143.5121   $143.51   $143.50   $143.50  
  Purchase #7 $25.36   8.237%   $27.4489   $27.45   $27.45   $27.40  
  7 purchase totals = $897.38       $976.9292   $976.93   $976.90   $976.90