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 $58.49   11.561%   $65.252   $65.25   $65.25   $65.30  
  Purchase #2 $45.74   7.112%   $48.993   $48.99   $49.00   $49.00  
  Purchase #3 $113.54   7.858%   $122.462   $122.46   $122.45   $122.50  
  Purchase #4 $141.83   6.860%   $151.5595   $151.56   $151.55   $151.60  
  Purchase #5 $140.71   7.547%   $151.3294   $151.33   $151.35   $151.30  
  Purchase #6 $135.97   9.269%   $148.5731   $148.57   $148.55   $148.60  
  Purchase #7 $205.35   3.245%   $212.0136   $212.01   $212.00   $212.00  
  7 purchase totals = $841.63       $900.1826   $900.17   $900.15   $900.30