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	$198.66	6.778%	$212.1252	$212.13	$212.15	$212.10
Purchase #2	$80.38	6.813%	$85.8563	$85.86	$85.85	$85.90
Purchase #3	$141.47	12.409%	$159.025	$159.03	$159.05	$159.00
Purchase #4	$212.89	5.173%	$223.9028	$223.90	$223.90	$223.90
Purchase #5	$37.82	11.193%	$42.0532	$42.05	$42.05	$42.10
Purchase #6	$74.58	6.490%	$79.4202	$79.42	$79.40	$79.40
Purchase #7	$98.69	12.539%	$111.0647	$111.06	$111.05	$111.10
7 purchase totals =	$844.49		$913.4474	$913.45	$913.45	$913.50