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	$233.72	4.790%	$244.9152	$244.92	$244.90	$244.90
Purchase #2	$79.85	7.636%	$85.9473	$85.95	$85.95	$85.90
Purchase #3	$197.40	12.563%	$222.1994	$222.20	$222.20	$222.20
Purchase #4	$82.57	11.138%	$91.7666	$91.77	$91.75	$91.80
Purchase #5	$188.29	5.202%	$198.0848	$198.08	$198.10	$198.10
Purchase #6	$46.84	5.362%	$49.3516	$49.35	$49.35	$49.40
Purchase #7	$35.61	12.506%	$40.0634	$40.06	$40.05	$40.10
7 purchase totals =	$864.28		$932.3283	$932.33	$932.30	$932.40