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 $177.55   13.768%   $201.9951   $202.00   $202.00   $202.00  
  Purchase #2 $106.41   3.661%   $110.3057   $110.31   $110.30   $110.30  
  Purchase #3 $52.90   13.140%   $59.8511   $59.85   $59.85   $59.90  
  Purchase #4 $49.33   12.405%   $55.4494   $55.45   $55.45   $55.40  
  Purchase #5 $235.86   8.278%   $255.3845   $255.38   $255.40   $255.40  
  Purchase #6 $239.47   9.392%   $261.961   $261.96   $261.95   $262.00  
  Purchase #7 $26.40   3.114%   $27.2221   $27.22   $27.20   $27.20  
  7 purchase totals = $887.92       $972.1689   $972.17   $972.15   $972.20