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 $143.39   5.118%   $150.7287   $150.73   $150.75   $150.70  
  Purchase #2 $231.95   13.380%   $262.9849   $262.98   $263.00   $263.00  
  Purchase #3 $26.25   13.835%   $29.8817   $29.88   $29.90   $29.90  
  Purchase #4 $215.61   3.505%   $223.1671   $223.17   $223.15   $223.20  
  Purchase #5 $53.58   8.241%   $57.9955   $58.00   $58.00   $58.00  
  Purchase #6 $100.68   6.671%   $107.3964   $107.40   $107.40   $107.40  
  Purchase #7 $97.28   3.374%   $100.5622   $100.56   $100.55   $100.60  
  7 purchase totals = $868.74       $932.7165   $932.72   $932.75   $932.80