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 $188.89   4.425%   $197.2484   $197.25   $197.25   $197.20  
  Purchase #2 $177.41   12.547%   $199.6696   $199.67   $199.65   $199.70  
  Purchase #3 $109.39   8.670%   $118.8741   $118.87   $118.85   $118.90  
  Purchase #4 $122.94   11.150%   $136.6478   $136.65   $136.65   $136.60  
  Purchase #5 $65.33   3.340%   $67.512   $67.51   $67.50   $67.50  
  Purchase #6 $52.34   9.119%   $57.1129   $57.11   $57.10   $57.10  
  Purchase #7 $223.49   8.577%   $242.6587   $242.66   $242.65   $242.70  
  7 purchase totals = $939.79       $1,019.7235   $1,019.72   $1,019.65   $1,019.70