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 $54.89   10.549%   $60.6803   $60.68   $60.70   $60.70  
  Purchase #2 $192.74   3.608%   $199.6941   $199.69   $199.70   $199.70  
  Purchase #3 $55.36   3.192%   $57.1271   $57.13   $57.15   $57.10  
  Purchase #4 $93.94   5.352%   $98.9677   $98.97   $98.95   $99.00  
  Purchase #5 $230.49   4.737%   $241.4083   $241.41   $241.40   $241.40  
  Purchase #6 $137.60   11.688%   $153.6827   $153.68   $153.70   $153.70  
  Purchase #7 $43.56   10.683%   $48.2135   $48.21   $48.20   $48.20  
  7 purchase totals = $808.58       $859.7737   $859.77   $859.80   $859.80