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 $73.58   5.114%   $77.3429   $77.34   $77.35   $77.30  
  Purchase #2 $117.81   13.314%   $133.4952   $133.50   $133.50   $133.50  
  Purchase #3 $178.39   8.463%   $193.4871   $193.49   $193.50   $193.50  
  Purchase #4 $96.64   3.234%   $99.7653   $99.77   $99.75   $99.80  
  Purchase #5 $104.87   3.639%   $108.6862   $108.69   $108.70   $108.70  
  Purchase #6 $188.51   13.290%   $213.563   $213.56   $213.55   $213.60  
  Purchase #7 $85.60   12.175%   $96.0218   $96.02   $96.00   $96.00  
  7 purchase totals = $845.40       $922.3615   $922.37   $922.35   $922.40