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	$169.61	12.165%	$190.2431	$190.24	$190.25	$190.20
Purchase #2	$37.72	12.280%	$42.352	$42.35	$42.35	$42.40
Purchase #3	$139.91	10.210%	$154.1948	$154.19	$154.20	$154.20
Purchase #4	$126.87	11.369%	$141.2939	$141.29	$141.30	$141.30
Purchase #5	$190.32	3.342%	$196.6805	$196.68	$196.70	$196.70
Purchase #6	$95.72	5.708%	$101.1837	$101.18	$101.20	$101.20
Purchase #7	$7.94	7.274%	$8.5176	$8.52	$8.50	$8.50
7 purchase totals =	$768.09		$834.4656	$834.45	$834.50	$834.50