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 $141.81   11.476%   $158.0841   $158.08   $158.10   $158.10  
  Purchase #2 $177.35   13.815%   $201.8509   $201.85   $201.85   $201.90  
  Purchase #3 $56.28   3.581%   $58.2954   $58.30   $58.30   $58.30  
  Purchase #4 $217.25   11.632%   $242.5205   $242.52   $242.50   $242.50  
  Purchase #5 $104.68   13.557%   $118.8715   $118.87   $118.85   $118.90  
  Purchase #6 $8.67   9.342%   $9.48   $9.48   $9.50   $9.50  
  Purchase #7 $42.59   3.770%   $44.1956   $44.20   $44.20   $44.20  
  7 purchase totals = $748.63       $833.2980   $833.30   $833.30   $833.40