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	$91.73	12.500%	$103.1963	$103.20	$103.20	$103.20
Purchase #2	$48.48	6.848%	$51.7999	$51.80	$51.80	$51.80
Purchase #3	$99.30	6.305%	$105.5609	$105.56	$105.55	$105.60
Purchase #4	$14.47	7.138%	$15.5029	$15.50	$15.50	$15.50
Purchase #5	$75.88	8.179%	$82.0862	$82.09	$82.10	$82.10
Purchase #6	$242.92	10.107%	$267.4719	$267.47	$267.45	$267.50
Purchase #7	$147.91	7.837%	$159.5017	$159.50	$159.50	$159.50
7 purchase totals =	$720.69		$785.1198	$785.12	$785.10	$785.20