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	$122.51	13.352%	$138.8675	$138.87	$138.85	$138.90
Purchase #2	$127.63	11.199%	$141.9233	$141.92	$141.90	$141.90
Purchase #3	$104.76	4.852%	$109.843	$109.84	$109.85	$109.80
Purchase #4	$220.95	7.746%	$238.0648	$238.06	$238.05	$238.10
Purchase #5	$165.37	4.814%	$173.3309	$173.33	$173.35	$173.30
Purchase #6	$168.86	12.596%	$190.1296	$190.13	$190.15	$190.10
Purchase #7	$243.25	8.284%	$263.4008	$263.40	$263.40	$263.40
7 purchase totals =	$1,153.33		$1,255.5599	$1,255.55	$1,255.55	$1,255.50