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	$186.69	12.813%	$210.6106	$210.61	$210.60	$210.60
Purchase #2	$82.28	8.845%	$89.5577	$89.56	$89.55	$89.60
Purchase #3	$195.75	3.209%	$202.0316	$202.03	$202.05	$202.00
Purchase #4	$142.37	3.567%	$147.4483	$147.45	$147.45	$147.40
Purchase #5	$60.83	11.360%	$67.7403	$67.74	$67.75	$67.70
Purchase #6	$42.97	8.390%	$46.5752	$46.58	$46.60	$46.60
Purchase #7	$59.75	4.775%	$62.6031	$62.60	$62.60	$62.60
7 purchase totals =	$770.64		$826.5668	$826.57	$826.60	$826.50