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 $50.56   5.313%   $53.2463   $53.25   $53.25   $53.20  
  Purchase #2 $245.86   4.137%   $256.0312   $256.03   $256.05   $256.00  
  Purchase #3 $82.98   11.861%   $92.8223   $92.82   $92.80   $92.80  
  Purchase #4 $80.72   5.650%   $85.2807   $85.28   $85.30   $85.30  
  Purchase #5 $184.70   4.792%   $193.5508   $193.55   $193.55   $193.60  
  Purchase #6 $160.53   11.510%   $179.007   $179.01   $179.00   $179.00  
  Purchase #7 $114.79   8.871%   $124.973   $124.97   $124.95   $125.00  
  7 purchase totals = $920.14       $984.9113   $984.91   $984.90   $984.90