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 $68.56   7.562%   $73.7445   $73.74   $73.75   $73.70  
  Purchase #2 $57.86   7.796%   $62.3708   $62.37   $62.35   $62.40  
  Purchase #3 $189.53   12.858%   $213.8998   $213.90   $213.90   $213.90  
  Purchase #4 $21.68   11.648%   $24.2053   $24.21   $24.20   $24.20  
  Purchase #5 $101.91   8.197%   $110.2636   $110.26   $110.25   $110.30  
  Purchase #6 $235.74   4.713%   $246.8504   $246.85   $246.85   $246.90  
  Purchase #7 $77.59   5.422%   $81.7969   $81.80   $81.80   $81.80  
  7 purchase totals = $752.87       $813.1313   $813.13   $813.10   $813.20