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 $152.49   5.680%   $161.1514   $161.15   $161.15   $161.20  
  Purchase #2 $110.77   7.782%   $119.3901   $119.39   $119.40   $119.40  
  Purchase #3 $25.83   7.727%   $27.8259   $27.83   $27.85   $27.80  
  Purchase #4 $166.61   5.691%   $176.0918   $176.09   $176.10   $176.10  
  Purchase #5 $121.60   3.227%   $125.524   $125.52   $125.50   $125.50  
  Purchase #6 $91.92   6.175%   $97.5961   $97.60   $97.60   $97.60  
  Purchase #7 $143.65   11.189%   $159.723   $159.72   $159.70   $159.70  
  7 purchase totals = $812.87       $867.3023   $867.30   $867.30   $867.30