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 $67.29   4.106%   $70.0529   $70.05   $70.05   $70.10  
  Purchase #2 $143.45   4.720%   $150.2208   $150.22   $150.20   $150.20  
  Purchase #3 $187.86   12.583%   $211.4984   $211.50   $211.50   $211.50  
  Purchase #4 $14.28   10.840%   $15.828   $15.83   $15.85   $15.80  
  Purchase #5 $245.97   12.320%   $276.2735   $276.27   $276.25   $276.30  
  Purchase #6 $238.64   5.387%   $251.4955   $251.50   $251.50   $251.50  
  Purchase #7 $43.57   6.159%   $46.2535   $46.25   $46.25   $46.30  
  7 purchase totals = $941.06       $1,021.6226   $1,021.62   $1,021.60   $1,021.70