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 $54.64   10.647%   $60.4575   $60.46   $60.45   $60.50  
  Purchase #2 $117.26   13.289%   $132.8427   $132.84   $132.85   $132.80  
  Purchase #3 $141.45   4.334%   $147.5804   $147.58   $147.60   $147.60  
  Purchase #4 $232.44   13.536%   $263.9031   $263.90   $263.90   $263.90  
  Purchase #5 $88.89   5.827%   $94.0696   $94.07   $94.05   $94.10  
  Purchase #6 $25.74   7.549%   $27.6831   $27.68   $27.70   $27.70  
  Purchase #7 $22.76   13.288%   $25.7843   $25.78   $25.80   $25.80  
  7 purchase totals = $683.18       $752.3207   $752.31   $752.35   $752.40