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 $52.86   10.589%   $58.4573   $58.46   $58.45   $58.50  
  Purchase #2 $162.91   7.651%   $175.3742   $175.37   $175.35   $175.40  
  Purchase #3 $231.92   7.598%   $249.5413   $249.54   $249.55   $249.50  
  Purchase #4 $101.47   5.633%   $107.1858   $107.19   $107.20   $107.20  
  Purchase #5 $41.73   3.222%   $43.0745   $43.07   $43.05   $43.10  
  Purchase #6 $22.58   13.696%   $25.6726   $25.67   $25.65   $25.70  
  Purchase #7 $164.73   7.364%   $176.8607   $176.86   $176.85   $176.90  
  7 purchase totals = $778.20       $836.1664   $836.16   $836.10   $836.30