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	$69.67	3.204%	$71.9022	$71.90	$71.90	$71.90
Purchase #2	$123.43	3.702%	$127.9994	$128.00	$128.00	$128.00
Purchase #3	$199.91	6.851%	$213.6058	$213.61	$213.60	$213.60
Purchase #4	$166.51	10.859%	$184.5913	$184.59	$184.60	$184.60
Purchase #5	$125.46	7.507%	$134.8783	$134.88	$134.90	$134.90
Purchase #6	$39.39	8.756%	$42.839	$42.84	$42.85	$42.80
Purchase #7	$186.46	9.772%	$204.6809	$204.68	$204.70	$204.70
7 purchase totals =	$910.83		$980.4969	$980.50	$980.55	$980.50