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   12.267%   $68.8309   $68.83   $68.85   $68.80  
  Purchase #2 $134.94   11.642%   $150.6497   $150.65   $150.65   $150.60  
  Purchase #3 $202.84   3.180%   $209.2903   $209.29   $209.30   $209.30  
  Purchase #4 $108.44   13.457%   $123.0328   $123.03   $123.05   $123.00  
  Purchase #5 $44.43   10.226%   $48.9734   $48.97   $48.95   $49.00  
  Purchase #6 $119.26   5.238%   $125.5068   $125.51   $125.50   $125.50  
  Purchase #7 $38.88   3.160%   $40.1086   $40.11   $40.10   $40.10  
  7 purchase totals = $710.10       $766.3925   $766.39   $766.40   $766.30