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 $51.50   11.819%   $57.5868   $57.59   $57.60   $57.60  
  Purchase #2 $109.33   5.870%   $115.7477   $115.75   $115.75   $115.70  
  Purchase #3 $167.83   11.403%   $186.9677   $186.97   $186.95   $187.00  
  Purchase #4 $137.67   9.124%   $150.231   $150.23   $150.25   $150.20  
  Purchase #5 $90.52   8.227%   $97.9671   $97.97   $97.95   $98.00  
  Purchase #6 $104.36   11.572%   $116.4365   $116.44   $116.45   $116.40  
  Purchase #7 $71.52   6.617%   $76.2525   $76.25   $76.25   $76.30  
  7 purchase totals = $732.73       $801.1893   $801.20   $801.20   $801.20