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 $86.25   11.256%   $95.9583   $95.96   $95.95   $96.00  
  Purchase #2 $31.99   12.457%   $35.975   $35.98   $36.00   $36.00  
  Purchase #3 $75.35   9.460%   $82.4781   $82.48   $82.50   $82.50  
  Purchase #4 $188.94   11.193%   $210.0881   $210.09   $210.10   $210.10  
  Purchase #5 $48.52   5.438%   $51.1585   $51.16   $51.15   $51.20  
  Purchase #6 $227.54   3.474%   $235.4447   $235.44   $235.45   $235.40  
  Purchase #7 $8.46   4.808%   $8.8668   $8.87   $8.85   $8.90  
  7 purchase totals = $667.05       $719.9695   $719.98   $720.00   $720.10