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 $50.37   7.713%   $54.255   $54.26   $54.25   $54.30  
  Purchase #2 $54.34   6.638%   $57.9471   $57.95   $57.95   $57.90  
  Purchase #3 $183.59   6.545%   $195.606   $195.61   $195.60   $195.60  
  Purchase #4 $223.85   12.364%   $251.5268   $251.53   $251.55   $251.50  
  Purchase #5 $12.37   5.287%   $13.024   $13.02   $13.00   $13.00  
  Purchase #6 $49.89   8.673%   $54.217   $54.22   $54.20   $54.20  
  Purchase #7 $221.27   11.203%   $246.0589   $246.06   $246.05   $246.10  
  7 purchase totals = $795.68       $872.6348   $872.65   $872.60   $872.60