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	$186.35	9.726%	$204.4744	$204.47	$204.45	$204.50
Purchase #2	$98.83	12.646%	$111.328	$111.33	$111.35	$111.30
Purchase #3	$6.76	7.321%	$7.2549	$7.25	$7.25	$7.30
Purchase #4	$196.74	4.837%	$206.2563	$206.26	$206.25	$206.30
Purchase #5	$40.73	3.206%	$42.0358	$42.04	$42.05	$42.00
Purchase #6	$180.64	6.713%	$192.7664	$192.77	$192.75	$192.80
Purchase #7	$165.92	12.796%	$187.1511	$187.15	$187.15	$187.20
7 purchase totals =	$875.97		$951.2669	$951.27	$951.25	$951.40