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 $169.58   13.637%   $192.7056   $192.71   $192.70   $192.70  
  Purchase #2 $18.42   12.679%   $20.7555   $20.76   $20.75   $20.80  
  Purchase #3 $136.37   13.595%   $154.9095   $154.91   $154.90   $154.90  
  Purchase #4 $108.63   8.425%   $117.7821   $117.78   $117.80   $117.80  
  Purchase #5 $224.67   5.261%   $236.4899   $236.49   $236.50   $236.50  
  Purchase #6 $117.97   9.165%   $128.782   $128.78   $128.80   $128.80  
  Purchase #7 $242.31   13.582%   $275.2205   $275.22   $275.20   $275.20  
  7 purchase totals = $1,017.95       $1,126.6451   $1,126.65   $1,126.65   $1,126.70