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 $26.86   11.176%   $29.8619   $29.86   $29.85   $29.90  
  Purchase #2 $120.63   5.771%   $127.5916   $127.59   $127.60   $127.60  
  Purchase #3 $68.25   10.805%   $75.6244   $75.62   $75.60   $75.60  
  Purchase #4 $95.91   6.313%   $101.9648   $101.96   $101.95   $102.00  
  Purchase #5 $196.61   12.411%   $221.0113   $221.01   $221.00   $221.00  
  Purchase #6 $34.54   11.113%   $38.3784   $38.38   $38.40   $38.40  
  Purchase #7 $158.44   10.147%   $174.5169   $174.52   $174.50   $174.50  
  7 purchase totals = $701.24       $768.9493   $768.94   $768.90   $769.00