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	$54.86	4.159%	$57.1416	$57.14	$57.15	$57.10
Purchase #2	$24.33	3.300%	$25.1329	$25.13	$25.15	$25.10
Purchase #3	$113.25	13.459%	$128.4923	$128.49	$128.50	$128.50
Purchase #4	$112.78	13.719%	$128.2523	$128.25	$128.25	$128.30
Purchase #5	$165.77	5.172%	$174.3436	$174.34	$174.35	$174.30
Purchase #6	$218.47	13.179%	$247.2622	$247.26	$247.25	$247.30
Purchase #7	$149.97	11.551%	$167.293	$167.29	$167.30	$167.30
7 purchase totals =	$839.43		$927.9179	$927.90	$927.95	$927.90