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 $88.62   5.495%   $93.4897   $93.49   $93.50   $93.50  
  Purchase #2 $32.41   11.205%   $36.0415   $36.04   $36.05   $36.00  
  Purchase #3 $237.53   13.556%   $269.7296   $269.73   $269.75   $269.70  
  Purchase #4 $218.44   9.308%   $238.7724   $238.77   $238.75   $238.80  
  Purchase #5 $220.78   5.692%   $233.3468   $233.35   $233.35   $233.30  
  Purchase #6 $46.45   13.164%   $52.5647   $52.56   $52.55   $52.60  
  Purchase #7 $106.45   7.272%   $114.191   $114.19   $114.20   $114.20  
  7 purchase totals = $950.68       $1,038.1357   $1,038.13   $1,038.15   $1,038.10