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 $189.86   4.577%   $198.5499   $198.55   $198.55   $198.50  
  Purchase #2 $167.31   6.116%   $177.5427   $177.54   $177.55   $177.50  
  Purchase #3 $196.96   10.441%   $217.5246   $217.52   $217.50   $217.50  
  Purchase #4 $95.26   6.854%   $101.7891   $101.79   $101.80   $101.80  
  Purchase #5 $71.79   5.313%   $75.6042   $75.60   $75.60   $75.60  
  Purchase #6 $206.71   7.347%   $221.897   $221.90   $221.90   $221.90  
  Purchase #7 $27.33   3.772%   $28.3609   $28.36   $28.35   $28.40  
  7 purchase totals = $955.22       $1,021.2684   $1,021.26   $1,021.25   $1,021.20