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	$160.63	3.102%	$165.6127	$165.61	$165.60	$165.60
Purchase #2	$89.77	11.555%	$100.1429	$100.14	$100.15	$100.10
Purchase #3	$168.25	6.153%	$178.6024	$178.60	$178.60	$178.60
Purchase #4	$31.51	6.603%	$33.5906	$33.59	$33.60	$33.60
Purchase #5	$222.91	12.412%	$250.5776	$250.58	$250.60	$250.60
Purchase #6	$204.83	8.712%	$222.6748	$222.67	$222.65	$222.70
Purchase #7	$180.30	4.383%	$188.2025	$188.20	$188.20	$188.20
7 purchase totals =	$1,058.20		$1,139.4035	$1,139.39	$1,139.40	$1,139.40