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 $244.69   3.173%   $252.454   $252.45   $252.45   $252.50  
  Purchase #2 $113.34   10.357%   $125.0786   $125.08   $125.10   $125.10  
  Purchase #3 $152.56   11.391%   $169.9381   $169.94   $169.95   $169.90  
  Purchase #4 $201.82   10.721%   $223.4571   $223.46   $223.45   $223.50  
  Purchase #5 $109.76   3.510%   $113.6126   $113.61   $113.60   $113.60  
  Purchase #6 $234.37   13.105%   $265.0842   $265.08   $265.10   $265.10  
  Purchase #7 $53.28   12.858%   $60.1307   $60.13   $60.15   $60.10  
  7 purchase totals = $1,109.82       $1,209.7553   $1,209.75   $1,209.80   $1,209.80