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 $236.33   11.538%   $263.5978   $263.60   $263.60   $263.60  
  Purchase #2 $54.26   11.729%   $60.6242   $60.62   $60.60   $60.60  
  Purchase #3 $171.55   9.125%   $187.2039   $187.20   $187.20   $187.20  
  Purchase #4 $22.28   10.427%   $24.6031   $24.60   $24.60   $24.60  
  Purchase #5 $194.29   8.853%   $211.4905   $211.49   $211.50   $211.50  
  Purchase #6 $160.88   13.493%   $182.5875   $182.59   $182.60   $182.60  
  Purchase #7 $114.26   8.781%   $124.2932   $124.29   $124.30   $124.30  
  7 purchase totals = $953.85       $1,054.4002   $1,054.39   $1,054.40   $1,054.40