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 $233.77   8.641%   $253.9701   $253.97   $253.95   $254.00  
  Purchase #2 $53.33   5.563%   $56.2967   $56.30   $56.30   $56.30  
  Purchase #3 $60.46   11.137%   $67.1934   $67.19   $67.20   $67.20  
  Purchase #4 $243.28   6.108%   $258.1395   $258.14   $258.15   $258.10  
  Purchase #5 $146.38   3.613%   $151.6687   $151.67   $151.65   $151.70  
  Purchase #6 $30.92   5.815%   $32.718   $32.72   $32.70   $32.70  
  Purchase #7 $114.62   13.756%   $130.3871   $130.39   $130.40   $130.40  
  7 purchase totals = $882.76       $950.3735   $950.38   $950.35   $950.40