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 $58.58   3.253%   $60.4856   $60.49   $60.50   $60.50  
  Purchase #2 $41.36   11.745%   $46.2177   $46.22   $46.20   $46.20  
  Purchase #3 $86.28   5.621%   $91.1298   $91.13   $91.15   $91.10  
  Purchase #4 $126.41   9.577%   $138.5163   $138.52   $138.50   $138.50  
  Purchase #5 $186.90   10.858%   $207.1936   $207.19   $207.20   $207.20  
  Purchase #6 $152.55   4.794%   $159.8632   $159.86   $159.85   $159.90  
  Purchase #7 $139.51   7.253%   $149.6287   $149.63   $149.65   $149.60  
  7 purchase totals = $791.59       $853.0349   $853.04   $853.05   $853.00