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 $240.62   9.556%   $263.6136   $263.61   $263.60   $263.60  
  Purchase #2 $173.38   3.145%   $178.8328   $178.83   $178.85   $178.80  
  Purchase #3 $19.87   12.639%   $22.3814   $22.38   $22.40   $22.40  
  Purchase #4 $84.67   10.262%   $93.3588   $93.36   $93.35   $93.40  
  Purchase #5 $169.53   13.576%   $192.5454   $192.55   $192.55   $192.50  
  Purchase #6 $232.51   12.154%   $260.7693   $260.77   $260.75   $260.80  
  Purchase #7 $204.62   10.203%   $225.4974   $225.50   $225.50   $225.50  
  7 purchase totals = $1,125.20       $1,236.9987   $1,237.00   $1,237.00   $1,237.00