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 $60.33   11.703%   $67.3904   $67.39   $67.40   $67.40  
  Purchase #2 $199.57   7.393%   $214.3242   $214.32   $214.30   $214.30  
  Purchase #3 $204.97   13.776%   $233.2067   $233.21   $233.20   $233.20  
  Purchase #4 $119.30   12.149%   $133.7938   $133.79   $133.80   $133.80  
  Purchase #5 $148.66   4.665%   $155.595   $155.60   $155.60   $155.60  
  Purchase #6 $48.65   6.295%   $51.7125   $51.71   $51.70   $51.70  
  Purchase #7 $210.49   12.225%   $236.2224   $236.22   $236.20   $236.20  
  7 purchase totals = $991.97       $1,092.2450   $1,092.24   $1,092.20   $1,092.20