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	$169.40	12.856%	$191.1781	$191.18	$191.20	$191.20
Purchase #2	$60.37	6.701%	$64.4154	$64.42	$64.40	$64.40
Purchase #3	$223.79	6.749%	$238.8936	$238.89	$238.90	$238.90
Purchase #4	$178.46	3.749%	$185.1505	$185.15	$185.15	$185.20
Purchase #5	$42.72	9.529%	$46.7908	$46.79	$46.80	$46.80
Purchase #6	$72.90	9.697%	$79.9691	$79.97	$79.95	$80.00
Purchase #7	$184.83	3.358%	$191.0366	$191.04	$191.05	$191.00
7 purchase totals =	$932.47		$997.4341	$997.44	$997.45	$997.50