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 $25.71   9.631%   $28.1861   $28.19   $28.20   $28.20  
  Purchase #2 $221.81   4.846%   $232.5589   $232.56   $232.55   $232.60  
  Purchase #3 $95.79   8.351%   $103.7894   $103.79   $103.80   $103.80  
  Purchase #4 $205.60   4.178%   $214.19   $214.19   $214.20   $214.20  
  Purchase #5 $69.64   6.556%   $74.2056   $74.21   $74.20   $74.20  
  Purchase #6 $136.29   13.651%   $154.8949   $154.89   $154.90   $154.90  
  Purchase #7 $143.36   3.787%   $148.789   $148.79   $148.80   $148.80  
  7 purchase totals = $898.20       $956.6139   $956.62   $956.65   $956.70