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 $55.30   13.627%   $62.8357   $62.84   $62.85   $62.80  
  Purchase #2 $68.66   11.375%   $76.4701   $76.47   $76.45   $76.50  
  Purchase #3 $247.71   11.277%   $275.6443   $275.64   $275.65   $275.60  
  Purchase #4 $200.63   8.671%   $218.0266   $218.03   $218.05   $218.00  
  Purchase #5 $159.77   5.279%   $168.2043   $168.20   $168.20   $168.20  
  Purchase #6 $10.92   6.343%   $11.6127   $11.61   $11.60   $11.60  
  Purchase #7 $42.40   8.467%   $45.99   $45.99   $46.00   $46.00  
  7 purchase totals = $785.39       $858.7837   $858.78   $858.80   $858.70