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 $132.77   11.505%   $148.0452   $148.05   $148.05   $148.00  
  Purchase #2 $201.95   12.575%   $227.3452   $227.35   $227.35   $227.30  
  Purchase #3 $164.37   10.682%   $181.928   $181.93   $181.95   $181.90  
  Purchase #4 $100.77   13.765%   $114.641   $114.64   $114.65   $114.60  
  Purchase #5 $148.82   5.666%   $157.2521   $157.25   $157.25   $157.30  
  Purchase #6 $66.59   10.406%   $73.5194   $73.52   $73.50   $73.50  
  Purchase #7 $124.43   7.253%   $133.4549   $133.45   $133.45   $133.50  
  7 purchase totals = $939.70       $1,036.1858   $1,036.19   $1,036.20   $1,036.10