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 $46.57   7.389%   $50.0111   $50.01   $50.00   $50.00  
  Purchase #2 $132.71   5.747%   $140.3368   $140.34   $140.35   $140.30  
  Purchase #3 $163.87   7.112%   $175.5244   $175.52   $175.50   $175.50  
  Purchase #4 $43.84   5.220%   $46.1284   $46.13   $46.15   $46.10  
  Purchase #5 $196.93   6.121%   $208.9841   $208.98   $209.00   $209.00  
  Purchase #6 $162.86   4.499%   $170.1871   $170.19   $170.20   $170.20  
  Purchase #7 $218.47   12.295%   $245.3309   $245.33   $245.35   $245.30  
  7 purchase totals = $965.25       $1,036.5028   $1,036.50   $1,036.55   $1,036.40