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 $93.97   4.606%   $98.2983   $98.30   $98.30   $98.30  
  Purchase #2 $124.71   6.753%   $133.1317   $133.13   $133.15   $133.10  
  Purchase #3 $179.89   6.681%   $191.9085   $191.91   $191.90   $191.90  
  Purchase #4 $203.97   7.751%   $219.7797   $219.78   $219.80   $219.80  
  Purchase #5 $178.37   10.485%   $197.0721   $197.07   $197.05   $197.10  
  Purchase #6 $163.86   6.663%   $174.778   $174.78   $174.80   $174.80  
  Purchase #7 $228.72   10.625%   $253.0215   $253.02   $253.00   $253.00  
  7 purchase totals = $1,173.49       $1,267.9898   $1,267.99   $1,268.00   $1,268.00