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 $246.39   6.624%   $262.7109   $262.71   $262.70   $262.70  
  Purchase #2 $250.32   5.391%   $263.8148   $263.81   $263.80   $263.80  
  Purchase #3 $19.63   3.568%   $20.3304   $20.33   $20.35   $20.30  
  Purchase #4 $210.37   4.782%   $220.4299   $220.43   $220.45   $220.40  
  Purchase #5 $191.29   13.446%   $217.0109   $217.01   $217.00   $217.00  
  Purchase #6 $55.76   12.661%   $62.8198   $62.82   $62.80   $62.80  
  Purchase #7 $148.43   6.422%   $157.9622   $157.96   $157.95   $158.00  
  7 purchase totals = $1,122.19       $1,205.0789   $1,205.07   $1,205.05   $1,205.00