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 $146.93   7.576%   $158.0614   $158.06   $158.05   $158.10  
  Purchase #2 $179.92   8.778%   $195.7134   $195.71   $195.70   $195.70  
  Purchase #3 $44.94   4.247%   $46.8486   $46.85   $46.85   $46.80  
  Purchase #4 $247.76   7.512%   $266.3717   $266.37   $266.35   $266.40  
  Purchase #5 $20.79   3.424%   $21.5018   $21.50   $21.50   $21.50  
  Purchase #6 $110.36   5.406%   $116.3261   $116.33   $116.35   $116.30  
  Purchase #7 $202.34   8.307%   $219.1484   $219.15   $219.15   $219.10  
  7 purchase totals = $953.04       $1,023.9714   $1,023.97   $1,023.95   $1,023.90