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 $229.53   5.397%   $241.9177   $241.92   $241.90   $241.90  
  Purchase #2 $150.61   4.495%   $157.3799   $157.38   $157.40   $157.40  
  Purchase #3 $59.69   4.533%   $62.3957   $62.40   $62.40   $62.40  
  Purchase #4 $219.89   3.809%   $228.2656   $228.27   $228.25   $228.30  
  Purchase #5 $211.60   3.563%   $219.1393   $219.14   $219.15   $219.10  
  Purchase #6 $220.75   5.527%   $232.9509   $232.95   $232.95   $233.00  
  Purchase #7 $163.68   13.788%   $186.2482   $186.25   $186.25   $186.20  
  7 purchase totals = $1,255.75       $1,328.2973   $1,328.31   $1,328.30   $1,328.30