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 $248.46   10.773%   $275.2266   $275.23   $275.25   $275.20  
  Purchase #2 $193.48   9.863%   $212.5629   $212.56   $212.55   $212.60  
  Purchase #3 $163.50   6.536%   $174.1864   $174.19   $174.20   $174.20  
  Purchase #4 $188.27   6.283%   $200.099   $200.10   $200.10   $200.10  
  Purchase #5 $233.28   8.584%   $253.3048   $253.30   $253.30   $253.30  
  Purchase #6 $123.47   8.212%   $133.6094   $133.61   $133.60   $133.60  
  Purchase #7 $131.25   8.586%   $142.5191   $142.52   $142.50   $142.50  
  7 purchase totals = $1,281.71       $1,391.5082   $1,391.51   $1,391.50   $1,391.50