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 $247.52   10.513%   $273.5418   $273.54   $273.55   $273.50  
  Purchase #2 $228.62   8.394%   $247.8104   $247.81   $247.80   $247.80  
  Purchase #3 $205.85   11.502%   $229.5269   $229.53   $229.55   $229.50  
  Purchase #4 $242.67   9.447%   $265.595   $265.60   $265.60   $265.60  
  Purchase #5 $73.64   7.194%   $78.9377   $78.94   $78.95   $78.90  
  Purchase #6 $224.85   11.592%   $250.9146   $250.91   $250.90   $250.90  
  Purchase #7 $119.81   11.768%   $133.9092   $133.91   $133.90   $133.90  
  7 purchase totals = $1,342.96       $1,480.2356   $1,480.24   $1,480.25   $1,480.10