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 $85.35   8.841%   $92.8958   $92.90   $92.90   $92.90  
  Purchase #2 $149.37   8.152%   $161.5466   $161.55   $161.55   $161.50  
  Purchase #3 $195.59   11.321%   $217.7327   $217.73   $217.75   $217.70  
  Purchase #4 $161.29   13.346%   $182.8158   $182.82   $182.80   $182.80  
  Purchase #5 $223.89   10.264%   $246.8701   $246.87   $246.85   $246.90  
  Purchase #6 $7.48   8.239%   $8.0963   $8.10   $8.10   $8.10  
  Purchase #7 $44.34   7.371%   $47.6083   $47.61   $47.60   $47.60  
  7 purchase totals = $867.31       $957.5656   $957.58   $957.55   $957.50