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	$133.43	12.500%	$150.1088	$150.11	$150.10	$150.10
Purchase #2	$100.98	7.750%	$108.806	$108.81	$108.80	$108.80
Purchase #3	$61.61	13.221%	$69.7555	$69.76	$69.75	$69.80
Purchase #4	$158.41	4.659%	$165.7903	$165.79	$165.80	$165.80
Purchase #5	$243.41	4.818%	$255.1375	$255.14	$255.15	$255.10
Purchase #6	$86.87	11.252%	$96.6446	$96.64	$96.65	$96.60
Purchase #7	$168.74	9.243%	$184.3366	$184.34	$184.35	$184.30
7 purchase totals =	$953.45		$1,030.5793	$1,030.59	$1,030.60	$1,030.50