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 $76.42   11.366%   $85.1059   $85.11   $85.10   $85.10  
  Purchase #2 $201.55   10.815%   $223.3476   $223.35   $223.35   $223.30  
  Purchase #3 $148.89   7.175%   $159.5729   $159.57   $159.55   $159.60  
  Purchase #4 $122.56   8.742%   $133.2742   $133.27   $133.25   $133.30  
  Purchase #5 $125.38   7.515%   $134.8023   $134.80   $134.80   $134.80  
  Purchase #6 $233.96   12.204%   $262.5125   $262.51   $262.50   $262.50  
  Purchase #7 $209.75   7.698%   $225.8966   $225.90   $225.90   $225.90  
  7 purchase totals = $1,118.51       $1,224.5120   $1,224.51   $1,224.45   $1,224.50