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 $34.81   5.756%   $36.8137   $36.81   $36.80   $36.80  
  Purchase #2 $147.28   4.721%   $154.2331   $154.23   $154.25   $154.20  
  Purchase #3 $97.67   6.134%   $103.6611   $103.66   $103.65   $103.70  
  Purchase #4 $240.75   13.446%   $273.1212   $273.12   $273.10   $273.10  
  Purchase #5 $153.55   12.289%   $172.4198   $172.42   $172.40   $172.40  
  Purchase #6 $61.66   8.442%   $66.8653   $66.87   $66.85   $66.90  
  Purchase #7 $140.49   4.593%   $146.9427   $146.94   $146.95   $146.90  
  7 purchase totals = $876.21       $954.0569   $954.05   $954.00   $954.00