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 $53.86   11.563%   $60.0878   $60.09   $60.10   $60.10  
  Purchase #2 $236.35   6.736%   $252.2705   $252.27   $252.25   $252.30  
  Purchase #3 $152.71   6.177%   $162.1429   $162.14   $162.15   $162.10  
  Purchase #4 $43.94   9.125%   $47.9495   $47.95   $47.95   $47.90  
  Purchase #5 $159.84   11.711%   $178.5589   $178.56   $178.55   $178.60  
  Purchase #6 $97.28   5.208%   $102.3463   $102.35   $102.35   $102.30  
  Purchase #7 $23.25   6.253%   $24.7038   $24.70   $24.70   $24.70  
  7 purchase totals = $767.23       $828.0597   $828.06   $828.05   $828.00