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 $101.76   8.254%   $110.1593   $110.16   $110.15   $110.20  
  Purchase #2 $5.89   5.252%   $6.1993   $6.20   $6.20   $6.20  
  Purchase #3 $108.59   7.290%   $116.5062   $116.51   $116.50   $116.50  
  Purchase #4 $152.45   6.238%   $161.9598   $161.96   $161.95   $162.00  
  Purchase #5 $67.89   9.422%   $74.2866   $74.29   $74.30   $74.30  
  Purchase #6 $196.58   4.283%   $204.9995   $205.00   $205.00   $205.00  
  Purchase #7 $118.27   7.668%   $127.3389   $127.34   $127.35   $127.30  
  7 purchase totals = $751.43       $801.4496   $801.46   $801.45   $801.50