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 $56.27   12.188%   $63.1282   $63.13   $63.15   $63.10  
  Purchase #2 $92.85   10.801%   $102.8787   $102.88   $102.90   $102.90  
  Purchase #3 $203.61   6.195%   $216.2236   $216.22   $216.20   $216.20  
  Purchase #4 $30.49   9.790%   $33.475   $33.48   $33.50   $33.50  
  Purchase #5 $95.46   9.624%   $104.6471   $104.65   $104.65   $104.60  
  Purchase #6 $206.79   13.843%   $235.4159   $235.42   $235.40   $235.40  
  Purchase #7 $210.94   4.356%   $220.1285   $220.13   $220.15   $220.10  
  7 purchase totals = $896.41       $975.8970   $975.91   $975.95   $975.80