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	$123.69	6.234%	$131.4008	$131.40	$131.40	$131.40
Purchase #2	$236.84	7.135%	$253.7385	$253.74	$253.75	$253.70
Purchase #3	$93.46	7.313%	$100.2947	$100.29	$100.30	$100.30
Purchase #4	$51.50	13.318%	$58.3588	$58.36	$58.35	$58.40
Purchase #5	$106.39	5.752%	$112.5096	$112.51	$112.50	$112.50
Purchase #6	$172.27	4.357%	$179.7758	$179.78	$179.80	$179.80
Purchase #7	$108.95	9.664%	$119.4789	$119.48	$119.50	$119.50
7 purchase totals =	$893.10		$955.5571	$955.56	$955.60	$955.60