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 $83.89   11.562%   $93.5894   $93.59   $93.60   $93.60  
  Purchase #2 $245.53   8.305%   $265.9213   $265.92   $265.90   $265.90  
  Purchase #3 $228.40   13.802%   $259.9238   $259.92   $259.90   $259.90  
  Purchase #4 $75.93   10.579%   $83.9626   $83.96   $83.95   $84.00  
  Purchase #5 $128.81   9.686%   $141.2865   $141.29   $141.30   $141.30  
  Purchase #6 $211.93   10.386%   $233.941   $233.94   $233.95   $233.90  
  Purchase #7 $21.89   9.383%   $23.9439   $23.94   $23.95   $23.90  
  7 purchase totals = $996.38       $1,102.5685   $1,102.56   $1,102.55   $1,102.50