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	$140.35	11.490%	$156.4762	$156.48	$156.50	$156.50
Purchase #2	$238.94	4.825%	$250.4689	$250.47	$250.45	$250.50
Purchase #3	$47.84	13.425%	$54.2625	$54.26	$54.25	$54.30
Purchase #4	$96.59	3.269%	$99.7475	$99.75	$99.75	$99.70
Purchase #5	$120.74	8.804%	$131.3699	$131.37	$131.35	$131.40
Purchase #6	$104.41	4.251%	$108.8485	$108.85	$108.85	$108.80
Purchase #7	$160.43	6.440%	$170.7617	$170.76	$170.75	$170.80
7 purchase totals =	$909.30		$971.9352	$971.94	$971.90	$972.00