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	$85.40	4.362%	$89.1251	$89.13	$89.15	$89.10
Purchase #2	$141.52	6.316%	$150.4584	$150.46	$150.45	$150.50
Purchase #3	$64.98	9.449%	$71.12	$71.12	$71.10	$71.10
Purchase #4	$67.93	7.127%	$72.7714	$72.77	$72.75	$72.80
Purchase #5	$205.48	7.741%	$221.3862	$221.39	$221.40	$221.40
Purchase #6	$149.90	5.250%	$157.7698	$157.77	$157.75	$157.80
Purchase #7	$125.90	11.247%	$140.06	$140.06	$140.05	$140.10
7 purchase totals =	$841.11		$902.6909	$902.70	$902.65	$902.80