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 $74.58   9.445%   $81.6241   $81.62   $81.60   $81.60  
  Purchase #2 $119.67   10.577%   $132.3275   $132.33   $132.35   $132.30  
  Purchase #3 $168.78   5.810%   $178.5861   $178.59   $178.60   $178.60  
  Purchase #4 $136.55   9.656%   $149.7353   $149.74   $149.75   $149.70  
  Purchase #5 $137.88   9.104%   $150.4326   $150.43   $150.45   $150.40  
  Purchase #6 $199.71   8.636%   $216.957   $216.96   $216.95   $217.00  
  Purchase #7 $153.59   8.545%   $166.7143   $166.71   $166.70   $166.70  
  7 purchase totals = $990.76       $1,076.3769   $1,076.38   $1,076.40   $1,076.30