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 $74.29   13.137%   $84.0495   $84.05   $84.05   $84.00  
  Purchase #2 $110.68   4.197%   $115.3252   $115.33   $115.35   $115.30  
  Purchase #3 $161.88   8.152%   $175.0765   $175.08   $175.10   $175.10  
  Purchase #4 $32.71   11.298%   $36.4056   $36.41   $36.40   $36.40  
  Purchase #5 $104.52   7.347%   $112.1991   $112.20   $112.20   $112.20  
  Purchase #6 $111.50   3.350%   $115.2353   $115.24   $115.25   $115.20  
  Purchase #7 $55.64   8.485%   $60.3611   $60.36   $60.35   $60.40  
  7 purchase totals = $651.22       $698.6523   $698.67   $698.70   $698.60