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 $23.84   6.329%   $25.3488   $25.35   $25.35   $25.30  
  Purchase #2 $149.87   12.777%   $169.0189   $169.02   $169.00   $169.00  
  Purchase #3 $177.74   4.844%   $186.3497   $186.35   $186.35   $186.30  
  Purchase #4 $229.98   8.690%   $249.9653   $249.97   $249.95   $250.00  
  Purchase #5 $63.37   12.429%   $71.2463   $71.25   $71.25   $71.20  
  Purchase #6 $204.81   11.697%   $228.7666   $228.77   $228.75   $228.80  
  Purchase #7 $115.66   7.186%   $123.9713   $123.97   $123.95   $124.00  
  7 purchase totals = $965.27       $1,054.6669   $1,054.68   $1,054.60   $1,054.60