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 $192.52   8.368%   $208.6301   $208.63   $208.65   $208.60  
  Purchase #2 $157.36   13.540%   $178.6665   $178.67   $178.65   $178.70  
  Purchase #3 $119.47   13.150%   $135.1803   $135.18   $135.20   $135.20  
  Purchase #4 $179.28   13.795%   $204.0117   $204.01   $204.00   $204.00  
  Purchase #5 $171.85   8.756%   $186.8972   $186.90   $186.90   $186.90  
  Purchase #6 $246.29   3.740%   $255.5012   $255.50   $255.50   $255.50  
  Purchase #7 $33.25   4.476%   $34.7383   $34.74   $34.75   $34.70  
  7 purchase totals = $1,100.02       $1,203.6253   $1,203.63   $1,203.65   $1,203.60