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 $47.32   13.141%   $53.5383   $53.54   $53.55   $53.50  
  Purchase #2 $248.96   9.532%   $272.6909   $272.69   $272.70   $272.70  
  Purchase #3 $173.94   5.538%   $183.5728   $183.57   $183.55   $183.60  
  Purchase #4 $239.93   4.331%   $250.3214   $250.32   $250.30   $250.30  
  Purchase #5 $73.34   9.676%   $80.4364   $80.44   $80.45   $80.40  
  Purchase #6 $43.73   7.764%   $47.1252   $47.13   $47.15   $47.10  
  Purchase #7 $65.73   6.446%   $69.967   $69.97   $69.95   $70.00  
  7 purchase totals = $892.95       $957.6520   $957.66   $957.65   $957.60