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	$172.83	5.825%	$182.8973	$182.90	$182.90	$182.90
Purchase #2	$101.61	10.136%	$111.9092	$111.91	$111.90	$111.90
Purchase #3	$148.51	12.474%	$167.0351	$167.04	$167.05	$167.00
Purchase #4	$228.35	9.344%	$249.687	$249.69	$249.70	$249.70
Purchase #5	$15.65	6.489%	$16.6655	$16.67	$16.65	$16.70
Purchase #6	$100.96	10.234%	$111.2922	$111.29	$111.30	$111.30
Purchase #7	$250.58	5.488%	$264.3318	$264.33	$264.35	$264.30
7 purchase totals =	$1,018.49		$1,103.8181	$1,103.83	$1,103.85	$1,103.80