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	$235.49	12.222%	$264.2716	$264.27	$264.25	$264.30
Purchase #2	$28.71	6.215%	$30.4943	$30.49	$30.50	$30.50
Purchase #3	$76.51	3.767%	$79.3921	$79.39	$79.40	$79.40
Purchase #4	$45.77	4.781%	$47.9583	$47.96	$47.95	$48.00
Purchase #5	$155.94	5.268%	$164.1549	$164.15	$164.15	$164.20
Purchase #6	$55.49	6.629%	$59.1684	$59.17	$59.15	$59.20
Purchase #7	$84.77	6.285%	$90.0978	$90.10	$90.10	$90.10
7 purchase totals =	$682.68		$735.5374	$735.53	$735.50	$735.70