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 $64.92   12.501%   $73.0356   $73.04   $73.05   $73.00  
  Purchase #2 $154.78   7.786%   $166.8312   $166.83   $166.85   $166.80  
  Purchase #3 $56.61   3.219%   $58.4323   $58.43   $58.45   $58.40  
  Purchase #4 $22.28   8.764%   $24.2326   $24.23   $24.25   $24.20  
  Purchase #5 $175.84   3.620%   $182.2054   $182.21   $182.20   $182.20  
  Purchase #6 $207.98   4.586%   $217.518   $217.52   $217.50   $217.50  
  Purchase #7 $16.26   10.436%   $17.9569   $17.96   $17.95   $18.00  
  7 purchase totals = $698.67       $740.2120   $740.22   $740.25   $740.10