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	$222.70	12.365%	$250.2369	$250.24	$250.25	$250.20
Purchase #2	$141.74	9.624%	$155.3811	$155.38	$155.40	$155.40
Purchase #3	$164.70	11.298%	$183.3078	$183.31	$183.30	$183.30
Purchase #4	$125.29	12.830%	$141.3647	$141.36	$141.35	$141.40
Purchase #5	$170.93	4.464%	$178.5603	$178.56	$178.55	$178.60
Purchase #6	$189.89	13.104%	$214.7732	$214.77	$214.75	$214.80
Purchase #7	$96.64	13.549%	$109.7338	$109.73	$109.75	$109.70
7 purchase totals =	$1,111.89		$1,233.3578	$1,233.35	$1,233.35	$1,233.40