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	$82.46	10.259%	$90.9196	$90.92	$90.90	$90.90
Purchase #2	$116.33	8.841%	$126.6147	$126.61	$126.60	$126.60
Purchase #3	$85.72	11.826%	$95.8572	$95.86	$95.85	$95.90
Purchase #4	$162.36	8.109%	$175.5258	$175.53	$175.55	$175.50
Purchase #5	$139.57	6.809%	$149.0733	$149.07	$149.05	$149.10
Purchase #6	$239.89	9.765%	$263.3153	$263.32	$263.30	$263.30
Purchase #7	$180.82	8.359%	$195.9347	$195.93	$195.95	$195.90
7 purchase totals =	$1,007.15		$1,097.2406	$1,097.24	$1,097.20	$1,097.20