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 $32.92   3.209%   $33.9764   $33.98   $34.00   $34.00  
  Purchase #2 $80.57   9.806%   $88.4707   $88.47   $88.45   $88.50  
  Purchase #3 $23.66   8.214%   $25.6034   $25.60   $25.60   $25.60  
  Purchase #4 $22.26   12.646%   $25.075   $25.08   $25.10   $25.10  
  Purchase #5 $62.57   8.181%   $67.6889   $67.69   $67.70   $67.70  
  Purchase #6 $165.81   10.710%   $183.5683   $183.57   $183.55   $183.60  
  Purchase #7 $186.38   11.311%   $207.4614   $207.46   $207.45   $207.50  
  7 purchase totals = $574.17       $631.8441   $631.85   $631.85   $632.00