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 $246.43   3.294%   $254.5474   $254.55   $254.55   $254.50  
  Purchase #2 $41.29   4.437%   $43.122   $43.12   $43.10   $43.10  
  Purchase #3 $175.71   13.607%   $199.6189   $199.62   $199.60   $199.60  
  Purchase #4 $194.60   11.329%   $216.6462   $216.65   $216.65   $216.60  
  Purchase #5 $46.50   4.512%   $48.5981   $48.60   $48.60   $48.60  
  Purchase #6 $13.25   12.264%   $14.875   $14.88   $14.90   $14.90  
  Purchase #7 $177.52   7.553%   $190.9281   $190.93   $190.95   $190.90  
  7 purchase totals = $895.30       $968.3357   $968.35   $968.35   $968.20