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 $32.77   11.149%   $36.4235   $36.42   $36.40   $36.40  
  Purchase #2 $41.98   7.341%   $45.0618   $45.06   $45.05   $45.10  
  Purchase #3 $236.28   13.799%   $268.8843   $268.88   $268.90   $268.90  
  Purchase #4 $133.28   5.448%   $140.5411   $140.54   $140.55   $140.50  
  Purchase #5 $212.31   4.250%   $221.3332   $221.33   $221.35   $221.30  
  Purchase #6 $211.61   3.282%   $218.555   $218.56   $218.55   $218.60  
  Purchase #7 $130.88   9.407%   $143.1919   $143.19   $143.20   $143.20  
  7 purchase totals = $999.11       $1,073.9908   $1,073.98   $1,074.00   $1,074.00