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 $62.42   5.769%   $66.021   $66.02   $66.00   $66.00  
  Purchase #2 $211.68   3.202%   $218.458   $218.46   $218.45   $218.50  
  Purchase #3 $72.26   12.607%   $81.3698   $81.37   $81.35   $81.40  
  Purchase #4 $197.35   4.440%   $206.1123   $206.11   $206.10   $206.10  
  Purchase #5 $178.35   10.604%   $197.2622   $197.26   $197.25   $197.30  
  Purchase #6 $85.43   5.190%   $89.8638   $89.86   $89.85   $89.90  
  Purchase #7 $158.93   3.833%   $165.0218   $165.02   $165.00   $165.00  
  7 purchase totals = $966.42       $1,024.1089   $1,024.10   $1,024.00   $1,024.20