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 $194.96   8.693%   $211.9079   $211.91   $211.90   $211.90  
  Purchase #2 $16.72   11.192%   $18.5913   $18.59   $18.60   $18.60  
  Purchase #3 $130.56   7.832%   $140.7855   $140.79   $140.80   $140.80  
  Purchase #4 $220.76   10.606%   $244.1738   $244.17   $244.15   $244.20  
  Purchase #5 $224.49   5.828%   $237.5733   $237.57   $237.55   $237.60  
  Purchase #6 $71.67   3.538%   $74.2057   $74.21   $74.20   $74.20  
  Purchase #7 $102.85   13.471%   $116.7049   $116.70   $116.70   $116.70  
  7 purchase totals = $962.01       $1,043.9424   $1,043.94   $1,043.90   $1,044.00