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 $177.27   12.451%   $199.3419   $199.34   $199.35   $199.30  
  Purchase #2 $244.99   6.756%   $261.5415   $261.54   $261.55   $261.50  
  Purchase #3 $236.52   4.310%   $246.714   $246.71   $246.70   $246.70  
  Purchase #4 $118.60   13.576%   $134.7011   $134.70   $134.70   $134.70  
  Purchase #5 $203.65   8.453%   $220.8645   $220.86   $220.85   $220.90  
  Purchase #6 $164.38   8.591%   $178.5019   $178.50   $178.50   $178.50  
  Purchase #7 $202.25   4.120%   $210.5827   $210.58   $210.60   $210.60  
  7 purchase totals = $1,347.66       $1,452.2476   $1,452.23   $1,452.25   $1,452.20