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	$6.42	12.781%	$7.2405	$7.24	$7.25	$7.20
Purchase #2	$36.39	3.470%	$37.6527	$37.65	$37.65	$37.70
Purchase #3	$56.78	13.767%	$64.5969	$64.60	$64.60	$64.60
Purchase #4	$132.58	10.570%	$146.5937	$146.59	$146.60	$146.60
Purchase #5	$248.76	11.580%	$277.5664	$277.57	$277.55	$277.60
Purchase #6	$63.95	4.742%	$66.9825	$66.98	$67.00	$67.00
Purchase #7	$83.36	11.369%	$92.8372	$92.84	$92.85	$92.80
7 purchase totals =	$628.24		$693.4699	$693.47	$693.50	$693.50