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 $168.87   13.547%   $191.7468   $191.75   $191.75   $191.70  
  Purchase #2 $157.83   5.794%   $166.9747   $166.97   $166.95   $167.00  
  Purchase #3 $212.34   11.404%   $236.5553   $236.56   $236.55   $236.60  
  Purchase #4 $196.93   11.216%   $219.0177   $219.02   $219.00   $219.00  
  Purchase #5 $93.57   13.426%   $106.1327   $106.13   $106.15   $106.10  
  Purchase #6 $106.50   3.306%   $110.0209   $110.02   $110.00   $110.00  
  Purchase #7 $184.29   3.387%   $190.5319   $190.53   $190.55   $190.50  
  7 purchase totals = $1,120.33       $1,220.9800   $1,220.98   $1,220.95   $1,220.90