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	$88.28	12.236%	$99.0819	$99.08	$99.10	$99.10
Purchase #2	$155.47	4.440%	$162.3729	$162.37	$162.35	$162.40
Purchase #3	$40.63	4.614%	$42.5047	$42.50	$42.50	$42.50
Purchase #4	$56.74	4.265%	$59.16	$59.16	$59.15	$59.20
Purchase #5	$178.83	12.694%	$201.5307	$201.53	$201.55	$201.50
Purchase #6	$70.82	11.560%	$79.0068	$79.01	$79.00	$79.00
Purchase #7	$124.33	4.586%	$130.0318	$130.03	$130.05	$130.00
7 purchase totals =	$715.10		$773.6888	$773.68	$773.70	$773.70