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 $126.97   11.307%   $141.3265   $141.33   $141.35   $141.30  
  Purchase #2 $58.70   4.207%   $61.1695   $61.17   $61.15   $61.20  
  Purchase #3 $94.37   7.765%   $101.6978   $101.70   $101.70   $101.70  
  Purchase #4 $91.98   5.732%   $97.2523   $97.25   $97.25   $97.30  
  Purchase #5 $219.61   11.626%   $245.1419   $245.14   $245.15   $245.10  
  Purchase #6 $205.34   9.528%   $224.9048   $224.90   $224.90   $224.90  
  Purchase #7 $139.56   8.160%   $150.9481   $150.95   $150.95   $150.90  
  7 purchase totals = $936.53       $1,022.4409   $1,022.44   $1,022.45   $1,022.40