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 $63.69   9.390%   $69.6705   $69.67   $69.65   $69.70  
  Purchase #2 $217.98   3.168%   $224.8856   $224.89   $224.90   $224.90  
  Purchase #3 $48.68   12.264%   $54.6501   $54.65   $54.65   $54.70  
  Purchase #4 $119.28   4.306%   $124.4162   $124.42   $124.40   $124.40  
  Purchase #5 $65.68   13.499%   $74.5461   $74.55   $74.55   $74.50  
  Purchase #6 $231.42   10.378%   $255.4368   $255.44   $255.45   $255.40  
  Purchase #7 $198.68   10.188%   $218.9215   $218.92   $218.90   $218.90  
  7 purchase totals = $945.41       $1,022.5268   $1,022.54   $1,022.50   $1,022.50