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 $196.46   3.150%   $202.6485   $202.65   $202.65   $202.60  
  Purchase #2 $173.73   11.339%   $193.4292   $193.43   $193.45   $193.40  
  Purchase #3 $157.32   10.824%   $174.3483   $174.35   $174.35   $174.30  
  Purchase #4 $242.92   12.457%   $273.1805   $273.18   $273.20   $273.20  
  Purchase #5 $126.79   10.496%   $140.0979   $140.10   $140.10   $140.10  
  Purchase #6 $140.31   10.804%   $155.4691   $155.47   $155.45   $155.50  
  Purchase #7 $132.82   5.526%   $140.1596   $140.16   $140.15   $140.20  
  7 purchase totals = $1,170.35       $1,279.3331   $1,279.34   $1,279.35   $1,279.30