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 $109.97   11.627%   $122.7562   $122.76   $122.75   $122.80  
  Purchase #2 $55.34   8.352%   $59.962   $59.96   $59.95   $60.00  
  Purchase #3 $29.87   5.743%   $31.5854   $31.59   $31.60   $31.60  
  Purchase #4 $222.99   4.293%   $232.563   $232.56   $232.55   $232.60  
  Purchase #5 $91.30   11.794%   $102.0679   $102.07   $102.05   $102.10  
  Purchase #6 $122.58   6.276%   $130.2731   $130.27   $130.25   $130.30  
  Purchase #7 $54.29   5.590%   $57.3248   $57.32   $57.30   $57.30  
  7 purchase totals = $686.34       $736.5324   $736.53   $736.45   $736.70