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 $82.33   12.176%   $92.3545   $92.35   $92.35   $92.40  
  Purchase #2 $46.35   8.273%   $50.1845   $50.18   $50.20   $50.20  
  Purchase #3 $88.90   9.690%   $97.5144   $97.51   $97.50   $97.50  
  Purchase #4 $225.50   9.402%   $246.7015   $246.70   $246.70   $246.70  
  Purchase #5 $192.35   3.710%   $199.4862   $199.49   $199.50   $199.50  
  Purchase #6 $204.44   5.867%   $216.4345   $216.43   $216.45   $216.40  
  Purchase #7 $222.82   11.578%   $248.6181   $248.62   $248.60   $248.60  
  7 purchase totals = $1,062.69       $1,151.2937   $1,151.28   $1,151.30   $1,151.30