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 $114.37   4.836%   $119.9009   $119.90   $119.90   $119.90  
  Purchase #2 $15.59   10.717%   $17.2608   $17.26   $17.25   $17.30  
  Purchase #3 $185.96   4.756%   $194.8043   $194.80   $194.80   $194.80  
  Purchase #4 $223.72   9.123%   $244.13   $244.13   $244.15   $244.10  
  Purchase #5 $153.36   4.296%   $159.9483   $159.95   $159.95   $159.90  
  Purchase #6 $103.55   4.732%   $108.45   $108.45   $108.45   $108.50  
  Purchase #7 $141.59   4.317%   $147.7024   $147.70   $147.70   $147.70  
  7 purchase totals = $938.14       $992.1967   $992.19   $992.20   $992.20