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 $241.78   12.293%   $271.502   $271.50   $271.50   $271.50  
  Purchase #2 $239.25   3.606%   $247.8774   $247.88   $247.90   $247.90  
  Purchase #3 $183.35   3.293%   $189.3877   $189.39   $189.40   $189.40  
  Purchase #4 $94.55   3.646%   $97.9973   $98.00   $98.00   $98.00  
  Purchase #5 $75.54   11.636%   $84.3298   $84.33   $84.35   $84.30  
  Purchase #6 $11.67   3.322%   $12.0577   $12.06   $12.05   $12.10  
  Purchase #7 $62.97   3.244%   $65.0127   $65.01   $65.00   $65.00  
  7 purchase totals = $909.11       $968.1646   $968.17   $968.20   $968.20