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 $224.81   8.544%   $244.0178   $244.02   $244.00   $244.00  
  Purchase #2 $38.81   6.662%   $41.3955   $41.40   $41.40   $41.40  
  Purchase #3 $204.85   11.375%   $228.1517   $228.15   $228.15   $228.20  
  Purchase #4 $164.93   6.548%   $175.7296   $175.73   $175.75   $175.70  
  Purchase #5 $191.56   7.354%   $205.6473   $205.65   $205.65   $205.60  
  Purchase #6 $87.72   12.803%   $98.9508   $98.95   $98.95   $99.00  
  Purchase #7 $249.51   12.346%   $280.3145   $280.31   $280.30   $280.30  
  7 purchase totals = $1,162.19       $1,274.2072   $1,274.21   $1,274.20   $1,274.20