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	$14.56	6.178%	$15.4595	$15.46	$15.45	$15.50
Purchase #2	$104.84	7.179%	$112.3665	$112.37	$112.35	$112.40
Purchase #3	$229.81	10.224%	$253.3058	$253.31	$253.30	$253.30
Purchase #4	$68.93	4.610%	$72.1077	$72.11	$72.10	$72.10
Purchase #5	$51.57	10.354%	$56.9096	$56.91	$56.90	$56.90
Purchase #6	$192.26	3.118%	$198.2547	$198.25	$198.25	$198.30
Purchase #7	$72.66	11.500%	$81.0159	$81.02	$81.00	$81.00
7 purchase totals =	$734.63		$789.4197	$789.43	$789.35	$789.50