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 $60.33   3.786%   $62.6141   $62.61   $62.60   $62.60  
  Purchase #2 $27.93   11.804%   $31.2269   $31.23   $31.25   $31.20  
  Purchase #3 $245.99   7.423%   $264.2498   $264.25   $264.25   $264.20  
  Purchase #4 $86.46   8.166%   $93.5203   $93.52   $93.50   $93.50  
  Purchase #5 $70.73   7.572%   $76.0857   $76.09   $76.10   $76.10  
  Purchase #6 $134.51   13.495%   $152.6621   $152.66   $152.65   $152.70  
  Purchase #7 $217.57   6.233%   $231.1311   $231.13   $231.15   $231.10  
  7 purchase totals = $843.52       $911.4900   $911.49   $911.50   $911.40