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 $137.80   10.218%   $151.8804   $151.88   $151.90   $151.90  
  Purchase #2 $41.51   11.716%   $46.3733   $46.37   $46.35   $46.40  
  Purchase #3 $75.52   10.697%   $83.5984   $83.60   $83.60   $83.60  
  Purchase #4 $20.74   6.136%   $22.0126   $22.01   $22.00   $22.00  
  Purchase #5 $186.70   4.234%   $194.6049   $194.60   $194.60   $194.60  
  Purchase #6 $156.87   13.706%   $178.3706   $178.37   $178.35   $178.40  
  Purchase #7 $137.50   6.661%   $146.6589   $146.66   $146.65   $146.70  
  7 purchase totals = $756.64       $823.4991   $823.49   $823.45   $823.60