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 $127.47   10.376%   $140.6963   $140.70   $140.70   $140.70  
  Purchase #2 $55.96   7.114%   $59.941   $59.94   $59.95   $59.90  
  Purchase #3 $111.97   8.490%   $121.4763   $121.48   $121.50   $121.50  
  Purchase #4 $140.38   8.874%   $152.8373   $152.84   $152.85   $152.80  
  Purchase #5 $24.70   7.290%   $26.5006   $26.50   $26.50   $26.50  
  Purchase #6 $202.98   7.317%   $217.832   $217.83   $217.85   $217.80  
  Purchase #7 $52.82   4.386%   $55.1367   $55.14   $55.15   $55.10  
  7 purchase totals = $716.28       $774.4202   $774.43   $774.50   $774.30