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	$38.77	9.599%	$42.4915	$42.49	$42.50	$42.50
Purchase #2	$84.66	11.657%	$94.5288	$94.53	$94.55	$94.50
Purchase #3	$102.35	7.222%	$109.7417	$109.74	$109.75	$109.70
Purchase #4	$47.48	12.381%	$53.3585	$53.36	$53.35	$53.40
Purchase #5	$176.42	3.427%	$182.4659	$182.47	$182.45	$182.50
Purchase #6	$206.59	6.774%	$220.5844	$220.58	$220.60	$220.60
Purchase #7	$122.94	7.196%	$131.7868	$131.79	$131.80	$131.80
7 purchase totals =	$779.21		$834.9576	$834.96	$835.00	$835.00