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	$204.60	3.425%	$211.6076	$211.61	$211.60	$211.60
Purchase #2	$83.89	9.279%	$91.6742	$91.67	$91.65	$91.70
Purchase #3	$236.82	5.697%	$250.3116	$250.31	$250.30	$250.30
Purchase #4	$19.44	4.213%	$20.259	$20.26	$20.25	$20.30
Purchase #5	$38.77	9.440%	$42.4299	$42.43	$42.45	$42.40
Purchase #6	$204.98	11.675%	$228.9114	$228.91	$228.90	$228.90
Purchase #7	$73.49	6.795%	$78.4836	$78.48	$78.50	$78.50
7 purchase totals =	$861.99		$923.6773	$923.67	$923.65	$923.70