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	$66.70	5.608%	$70.4405	$70.44	$70.45	$70.40
Purchase #2	$81.88	9.737%	$89.8527	$89.85	$89.85	$89.90
Purchase #3	$129.55	9.744%	$142.1734	$142.17	$142.15	$142.20
Purchase #4	$140.41	6.412%	$149.4131	$149.41	$149.40	$149.40
Purchase #5	$152.67	9.611%	$167.3431	$167.34	$167.35	$167.30
Purchase #6	$63.44	13.713%	$72.1395	$72.14	$72.15	$72.10
Purchase #7	$175.49	4.240%	$182.9308	$182.93	$182.95	$182.90
7 purchase totals =	$810.14		$874.2931	$874.28	$874.30	$874.20