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 $30.83   9.224%   $33.6738   $33.67   $33.65   $33.70  
  Purchase #2 $208.86   12.347%   $234.6479   $234.65   $234.65   $234.60  
  Purchase #3 $16.95   12.496%   $19.0681   $19.07   $19.05   $19.10  
  Purchase #4 $220.46   4.804%   $231.0509   $231.05   $231.05   $231.10  
  Purchase #5 $211.51   5.664%   $223.4899   $223.49   $223.50   $223.50  
  Purchase #6 $243.35   11.710%   $271.8463   $271.85   $271.85   $271.80  
  Purchase #7 $12.73   4.406%   $13.2909   $13.29   $13.30   $13.30  
  7 purchase totals = $944.69       $1,027.0678   $1,027.07   $1,027.05   $1,027.10