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	$50.72	4.813%	$53.1612	$53.16	$53.15	$53.20
Purchase #2	$37.42	7.632%	$40.2759	$40.28	$40.30	$40.30
Purchase #3	$25.86	5.807%	$27.3617	$27.36	$27.35	$27.40
Purchase #4	$146.88	12.373%	$165.0535	$165.05	$165.05	$165.10
Purchase #5	$101.90	9.324%	$111.4012	$111.40	$111.40	$111.40
Purchase #6	$78.69	9.497%	$86.1632	$86.16	$86.15	$86.20
Purchase #7	$115.42	12.498%	$129.8452	$129.85	$129.85	$129.80
7 purchase totals =	$556.89		$613.2619	$613.26	$613.25	$613.40