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 $32.88   11.113%   $36.534   $36.53   $36.55   $36.50  
  Purchase #2 $210.82   11.479%   $235.02   $235.02   $235.00   $235.00  
  Purchase #3 $39.44   3.611%   $40.8642   $40.86   $40.85   $40.90  
  Purchase #4 $62.52   13.516%   $70.9702   $70.97   $70.95   $71.00  
  Purchase #5 $213.59   9.823%   $234.5709   $234.57   $234.55   $234.60  
  Purchase #6 $119.50   4.564%   $124.954   $124.95   $124.95   $125.00  
  Purchase #7 $154.70   5.743%   $163.5844   $163.58   $163.60   $163.60  
  7 purchase totals = $833.45       $906.4977   $906.48   $906.45   $906.60