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 $48.25   10.132%   $53.1387   $53.14   $53.15   $53.10  
  Purchase #2 $167.94   7.757%   $180.9671   $180.97   $180.95   $181.00  
  Purchase #3 $119.57   12.155%   $134.1037   $134.10   $134.10   $134.10  
  Purchase #4 $89.97   12.575%   $101.2837   $101.28   $101.30   $101.30  
  Purchase #5 $153.26   12.413%   $172.2842   $172.28   $172.30   $172.30  
  Purchase #6 $227.45   9.551%   $249.1737   $249.17   $249.15   $249.20  
  Purchase #7 $76.40   4.481%   $79.8235   $79.82   $79.80   $79.80  
  7 purchase totals = $882.84       $970.7746   $970.76   $970.75   $970.80