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	$93.82	6.432%	$99.8545	$99.85	$99.85	$99.90
Purchase #2	$226.34	10.352%	$249.7707	$249.77	$249.75	$249.80
Purchase #3	$211.75	5.527%	$223.4534	$223.45	$223.45	$223.50
Purchase #4	$49.77	11.219%	$55.3537	$55.35	$55.35	$55.40
Purchase #5	$31.90	9.272%	$34.8578	$34.86	$34.85	$34.90
Purchase #6	$39.34	3.813%	$40.84	$40.84	$40.85	$40.80
Purchase #7	$247.89	11.870%	$277.3145	$277.31	$277.30	$277.30
7 purchase totals =	$900.81		$981.4446	$981.43	$981.40	$981.60