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 $247.51   11.267%   $275.397   $275.40   $275.40   $275.40  
  Purchase #2 $170.30   6.152%   $180.7769   $180.78   $180.80   $180.80  
  Purchase #3 $18.97   10.183%   $20.9017   $20.90   $20.90   $20.90  
  Purchase #4 $211.92   7.665%   $228.1637   $228.16   $228.15   $228.20  
  Purchase #5 $56.92   11.414%   $63.4168   $63.42   $63.40   $63.40  
  Purchase #6 $212.42   10.128%   $233.9339   $233.93   $233.95   $233.90  
  Purchase #7 $25.73   4.251%   $26.8238   $26.82   $26.80   $26.80  
  7 purchase totals = $943.77       $1,029.4138   $1,029.41   $1,029.40   $1,029.40