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 $194.71   11.299%   $216.7103   $216.71   $216.70   $216.70  
  Purchase #2 $31.61   8.399%   $34.2649   $34.26   $34.25   $34.30  
  Purchase #3 $101.51   6.537%   $108.1457   $108.15   $108.15   $108.10  
  Purchase #4 $190.81   7.650%   $205.407   $205.41   $205.40   $205.40  
  Purchase #5 $249.56   6.556%   $265.9212   $265.92   $265.90   $265.90  
  Purchase #6 $207.55   13.868%   $236.333   $236.33   $236.35   $236.30  
  Purchase #7 $23.59   8.812%   $25.6688   $25.67   $25.65   $25.70  
  7 purchase totals = $999.34       $1,092.4509   $1,092.45   $1,092.40   $1,092.40