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	$149.90	3.736%	$155.5003	$155.50	$155.50	$155.50
Purchase #2	$67.85	13.529%	$77.0294	$77.03	$77.05	$77.00
Purchase #3	$194.59	13.368%	$220.6028	$220.60	$220.60	$220.60
Purchase #4	$140.56	6.362%	$149.5024	$149.50	$149.50	$149.50
Purchase #5	$129.59	7.844%	$139.755	$139.76	$139.75	$139.80
Purchase #6	$74.83	12.148%	$83.9203	$83.92	$83.90	$83.90
Purchase #7	$166.86	3.621%	$172.902	$172.90	$172.90	$172.90
7 purchase totals =	$924.18		$999.2122	$999.21	$999.20	$999.20