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 $68.46   3.735%   $71.017   $71.02   $71.00   $71.00  
  Purchase #2 $69.54   6.333%   $73.944   $73.94   $73.95   $73.90  
  Purchase #3 $129.93   5.126%   $136.5902   $136.59   $136.60   $136.60  
  Purchase #4 $218.40   13.194%   $247.2157   $247.22   $247.20   $247.20  
  Purchase #5 $195.26   10.552%   $215.8638   $215.86   $215.85   $215.90  
  Purchase #6 $93.79   11.172%   $104.2682   $104.27   $104.25   $104.30  
  Purchase #7 $191.98   13.705%   $218.2909   $218.29   $218.30   $218.30  
  7 purchase totals = $967.36       $1,067.1898   $1,067.19   $1,067.15   $1,067.20