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 $67.42   4.227%   $70.2698   $70.27   $70.25   $70.30  
  Purchase #2 $24.62   9.337%   $26.9188   $26.92   $26.90   $26.90  
  Purchase #3 $157.66   8.362%   $170.8435   $170.84   $170.85   $170.80  
  Purchase #4 $34.89   5.519%   $36.8156   $36.82   $36.80   $36.80  
  Purchase #5 $116.34   13.234%   $131.7364   $131.74   $131.75   $131.70  
  Purchase #6 $124.94   8.458%   $135.5074   $135.51   $135.50   $135.50  
  Purchase #7 $169.43   13.448%   $192.2149   $192.21   $192.20   $192.20  
  7 purchase totals = $695.30       $764.3064   $764.31   $764.25   $764.20