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 $88.77   5.394%   $93.5583   $93.56   $93.55   $93.60  
  Purchase #2 $118.85   9.607%   $130.2679   $130.27   $130.25   $130.30  
  Purchase #3 $169.89   5.584%   $179.3767   $179.38   $179.40   $179.40  
  Purchase #4 $136.69   6.594%   $145.7033   $145.70   $145.70   $145.70  
  Purchase #5 $85.54   7.714%   $92.1386   $92.14   $92.15   $92.10  
  Purchase #6 $100.56   13.344%   $113.9787   $113.98   $114.00   $114.00  
  Purchase #7 $185.75   8.191%   $200.9648   $200.96   $200.95   $201.00  
  7 purchase totals = $886.05       $955.9883   $955.99   $956.00   $956.10