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	$201.35	13.433%	$228.3973	$228.40	$228.40	$228.40
Purchase #2	$138.65	4.513%	$144.9073	$144.91	$144.90	$144.90
Purchase #3	$27.56	12.668%	$31.0513	$31.05	$31.05	$31.10
Purchase #4	$186.27	5.480%	$196.4776	$196.48	$196.50	$196.50
Purchase #5	$85.60	11.363%	$95.3267	$95.33	$95.35	$95.30
Purchase #6	$24.99	7.841%	$26.9495	$26.95	$26.95	$26.90
Purchase #7	$247.89	12.519%	$278.9233	$278.92	$278.90	$278.90
7 purchase totals =	$912.31		$1,002.0330	$1,002.04	$1,002.05	$1,002.00