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	$243.74	12.417%	$274.0052	$274.01	$274.00	$274.00
Purchase #2	$144.44	11.113%	$160.4916	$160.49	$160.50	$160.50
Purchase #3	$27.59	5.301%	$29.0525	$29.05	$29.05	$29.10
Purchase #4	$66.41	8.582%	$72.1093	$72.11	$72.10	$72.10
Purchase #5	$196.36	10.150%	$216.2905	$216.29	$216.30	$216.30
Purchase #6	$129.90	13.354%	$147.2468	$147.25	$147.25	$147.20
Purchase #7	$229.88	9.400%	$251.4887	$251.49	$251.50	$251.50
7 purchase totals =	$1,038.32		$1,150.6846	$1,150.69	$1,150.70	$1,150.70