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 $61.46   11.645%   $68.617   $68.62   $68.60   $68.60  
  Purchase #2 $56.50   11.337%   $62.9054   $62.91   $62.90   $62.90  
  Purchase #3 $211.61   6.441%   $225.2398   $225.24   $225.25   $225.20  
  Purchase #4 $235.60   11.865%   $263.5539   $263.55   $263.55   $263.60  
  Purchase #5 $20.56   12.627%   $23.1561   $23.16   $23.15   $23.20  
  Purchase #6 $51.68   6.362%   $54.9679   $54.97   $54.95   $55.00  
  Purchase #7 $164.29   5.722%   $173.6907   $173.69   $173.70   $173.70  
  7 purchase totals = $801.70       $872.1308   $872.14   $872.10   $872.20