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 $232.67   11.664%   $259.8086   $259.81   $259.80   $259.80  
  Purchase #2 $249.98   4.298%   $260.7241   $260.72   $260.70   $260.70  
  Purchase #3 $41.97   4.327%   $43.786   $43.79   $43.80   $43.80  
  Purchase #4 $55.86   9.651%   $61.251   $61.25   $61.25   $61.30  
  Purchase #5 $23.85   9.525%   $26.1217   $26.12   $26.10   $26.10  
  Purchase #6 $95.91   7.226%   $102.8405   $102.84   $102.85   $102.80  
  Purchase #7 $17.97   4.694%   $18.8135   $18.81   $18.80   $18.80  
  7 purchase totals = $718.21       $773.3454   $773.34   $773.30   $773.30