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 $206.96   8.354%   $224.2494   $224.25   $224.25   $224.20  
  Purchase #2 $45.31   11.643%   $50.5854   $50.59   $50.60   $50.60  
  Purchase #3 $211.54   3.548%   $219.0454   $219.05   $219.05   $219.00  
  Purchase #4 $246.74   4.222%   $257.1574   $257.16   $257.15   $257.20  
  Purchase #5 $150.53   10.346%   $166.1038   $166.10   $166.10   $166.10  
  Purchase #6 $134.45   4.490%   $140.4868   $140.49   $140.50   $140.50  
  Purchase #7 $166.95   11.182%   $185.6183   $185.62   $185.60   $185.60  
  7 purchase totals = $1,162.48       $1,243.2465   $1,243.26   $1,243.25   $1,243.20