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 $29.94   11.811%   $33.4762   $33.48   $33.50   $33.50  
  Purchase #2 $188.93   12.195%   $211.97   $211.97   $211.95   $212.00  
  Purchase #3 $238.97   12.690%   $269.2953   $269.30   $269.30   $269.30  
  Purchase #4 $237.58   5.367%   $250.3309   $250.33   $250.35   $250.30  
  Purchase #5 $208.42   13.330%   $236.2024   $236.20   $236.20   $236.20  
  Purchase #6 $220.35   13.254%   $249.5552   $249.56   $249.55   $249.60  
  Purchase #7 $183.52   10.422%   $202.6465   $202.65   $202.65   $202.60  
  7 purchase totals = $1,307.71       $1,453.4765   $1,453.49   $1,453.50   $1,453.50