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 $88.70   5.681%   $93.739   $93.74   $93.75   $93.70  
  Purchase #2 $167.62   10.823%   $185.7615   $185.76   $185.75   $185.80  
  Purchase #3 $206.87   12.536%   $232.8032   $232.80   $232.80   $232.80  
  Purchase #4 $107.28   4.226%   $111.8137   $111.81   $111.80   $111.80  
  Purchase #5 $89.30   11.825%   $99.8597   $99.86   $99.85   $99.90  
  Purchase #6 $244.57   7.412%   $262.6975   $262.70   $262.70   $262.70  
  Purchase #7 $31.80   5.522%   $33.556   $33.56   $33.55   $33.60  
  7 purchase totals = $936.14       $1,020.2306   $1,020.23   $1,020.20   $1,020.30