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	$61.38	7.691%	$66.1007	$66.10	$66.10	$66.10
Purchase #2	$186.88	4.661%	$195.5905	$195.59	$195.60	$195.60
Purchase #3	$29.53	11.233%	$32.8471	$32.85	$32.85	$32.80
Purchase #4	$243.54	3.228%	$251.4015	$251.40	$251.40	$251.40
Purchase #5	$146.57	12.780%	$165.3016	$165.30	$165.30	$165.30
Purchase #6	$6.84	6.806%	$7.3055	$7.31	$7.30	$7.30
Purchase #7	$200.93	4.630%	$210.2331	$210.23	$210.25	$210.20
7 purchase totals =	$875.67		$928.7800	$928.78	$928.80	$928.70