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 $57.33   8.192%   $62.0265   $62.03   $62.05   $62.00  
  Purchase #2 $34.78   3.455%   $35.9816   $35.98   $36.00   $36.00  
  Purchase #3 $148.49   12.607%   $167.2101   $167.21   $167.20   $167.20  
  Purchase #4 $250.95   11.165%   $278.9686   $278.97   $278.95   $279.00  
  Purchase #5 $163.51   9.649%   $179.2871   $179.29   $179.30   $179.30  
  Purchase #6 $198.87   11.640%   $222.0185   $222.02   $222.00   $222.00  
  Purchase #7 $105.43   11.767%   $117.8359   $117.84   $117.85   $117.80  
  7 purchase totals = $959.36       $1,063.3283   $1,063.34   $1,063.35   $1,063.30