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	$78.47	8.473%	$85.1188	$85.12	$85.10	$85.10
Purchase #2	$135.53	11.316%	$150.8666	$150.87	$150.85	$150.90
Purchase #3	$227.62	9.109%	$248.3539	$248.35	$248.35	$248.40
Purchase #4	$212.40	7.479%	$228.2854	$228.29	$228.30	$228.30
Purchase #5	$125.71	10.828%	$139.3219	$139.32	$139.30	$139.30
Purchase #6	$153.89	12.746%	$173.5048	$173.50	$173.50	$173.50
Purchase #7	$181.85	9.694%	$199.4785	$199.48	$199.50	$199.50
7 purchase totals =	$1,115.47		$1,224.9299	$1,224.93	$1,224.90	$1,225.00