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 $113.84   12.602%   $128.1861   $128.19   $128.20   $128.20  
  Purchase #2 $134.56   9.143%   $146.8628   $146.86   $146.85   $146.90  
  Purchase #3 $176.93   5.504%   $186.6682   $186.67   $186.65   $186.70  
  Purchase #4 $220.84   5.379%   $232.719   $232.72   $232.70   $232.70  
  Purchase #5 $22.50   12.844%   $25.3899   $25.39   $25.40   $25.40  
  Purchase #6 $199.94   8.487%   $216.9089   $216.91   $216.90   $216.90  
  Purchase #7 $246.68   10.746%   $273.1882   $273.19   $273.20   $273.20  
  7 purchase totals = $1,115.29       $1,209.9231   $1,209.93   $1,209.90   $1,210.00