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 $69.77   10.310%   $76.9633   $76.96   $76.95   $77.00  
  Purchase #2 $24.33   10.629%   $26.916   $26.92   $26.90   $26.90  
  Purchase #3 $192.32   4.717%   $201.3917   $201.39   $201.40   $201.40  
  Purchase #4 $104.55   13.143%   $118.291   $118.29   $118.30   $118.30  
  Purchase #5 $151.94   4.671%   $159.0371   $159.04   $159.05   $159.00  
  Purchase #6 $53.63   5.330%   $56.4885   $56.49   $56.50   $56.50  
  Purchase #7 $102.88   13.687%   $116.9612   $116.96   $116.95   $117.00  
  7 purchase totals = $699.42       $756.0488   $756.05   $756.05   $756.10