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	$124.78	12.413%	$140.2689	$140.27	$140.25	$140.30
Purchase #2	$32.73	6.568%	$34.8797	$34.88	$34.90	$34.90
Purchase #3	$94.85	3.873%	$98.5235	$98.52	$98.50	$98.50
Purchase #4	$92.90	6.731%	$99.1531	$99.15	$99.15	$99.20
Purchase #5	$197.68	4.675%	$206.9215	$206.92	$206.90	$206.90
Purchase #6	$229.33	4.847%	$240.4456	$240.45	$240.45	$240.40
Purchase #7	$51.32	5.326%	$54.0533	$54.05	$54.05	$54.10
7 purchase totals =	$823.59		$874.2456	$874.24	$874.20	$874.30