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 $85.41   13.127%   $96.6218   $96.62   $96.60   $96.60  
  Purchase #2 $23.77   3.396%   $24.5772   $24.58   $24.60   $24.60  
  Purchase #3 $190.67   6.136%   $202.3695   $202.37   $202.35   $202.40  
  Purchase #4 $137.56   11.633%   $153.5624   $153.56   $153.55   $153.60  
  Purchase #5 $140.53   12.542%   $158.1553   $158.16   $158.15   $158.20  
  Purchase #6 $63.60   13.846%   $72.4061   $72.41   $72.40   $72.40  
  Purchase #7 $227.92   5.455%   $240.353   $240.35   $240.35   $240.40  
  7 purchase totals = $869.46       $948.0453   $948.05   $948.00   $948.20