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 $184.74   12.754%   $208.3017   $208.30   $208.30   $208.30  
  Purchase #2 $187.92   5.147%   $197.5922   $197.59   $197.60   $197.60  
  Purchase #3 $243.97   12.172%   $273.666   $273.67   $273.65   $273.70  
  Purchase #4 $215.87   7.674%   $232.4359   $232.44   $232.45   $232.40  
  Purchase #5 $194.48   3.291%   $200.8803   $200.88   $200.90   $200.90  
  Purchase #6 $24.42   11.621%   $27.2578   $27.26   $27.25   $27.30  
  Purchase #7 $99.77   11.682%   $111.4251   $111.43   $111.45   $111.40  
  7 purchase totals = $1,151.17       $1,251.5590   $1,251.57   $1,251.60   $1,251.60