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	$54.33	6.596%	$57.9136	$57.91	$57.90	$57.90
Purchase #2	$85.64	8.481%	$92.9031	$92.90	$92.90	$92.90
Purchase #3	$102.73	8.276%	$111.2319	$111.23	$111.25	$111.20
Purchase #4	$98.76	7.659%	$106.324	$106.32	$106.30	$106.30
Purchase #5	$21.90	13.462%	$24.8482	$24.85	$24.85	$24.80
Purchase #6	$248.66	11.146%	$276.3756	$276.38	$276.40	$276.40
Purchase #7	$135.44	6.111%	$143.7167	$143.72	$143.70	$143.70
7 purchase totals =	$747.46		$813.3131	$813.31	$813.30	$813.20