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 $61.31   9.500%   $67.1345   $67.13   $67.15   $67.10  
  Purchase #2 $188.92   11.661%   $210.95   $210.95   $210.95   $211.00  
  Purchase #3 $108.49   8.344%   $117.5424   $117.54   $117.55   $117.50  
  Purchase #4 $180.55   13.474%   $204.8773   $204.88   $204.90   $204.90  
  Purchase #5 $37.72   11.728%   $42.1438   $42.14   $42.15   $42.10  
  Purchase #6 $234.54   8.154%   $253.6644   $253.66   $253.65   $253.70  
  Purchase #7 $177.54   4.636%   $185.7708   $185.77   $185.75   $185.80  
  7 purchase totals = $989.07       $1,082.0832   $1,082.07   $1,082.10   $1,082.10