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 $58.39   13.424%   $66.2283   $66.23   $66.25   $66.20  
  Purchase #2 $208.78   9.794%   $229.2279   $229.23   $229.25   $229.20  
  Purchase #3 $43.36   3.662%   $44.9478   $44.95   $44.95   $44.90  
  Purchase #4 $112.33   8.547%   $121.9308   $121.93   $121.95   $121.90  
  Purchase #5 $215.64   12.289%   $242.14   $242.14   $242.15   $242.10  
  Purchase #6 $164.98   7.704%   $177.6901   $177.69   $177.70   $177.70  
  Purchase #7 $160.97   3.672%   $166.8808   $166.88   $166.90   $166.90  
  7 purchase totals = $964.45       $1,049.0457   $1,049.05   $1,049.15   $1,048.90