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	$222.86	9.431%	$243.8779	$243.88	$243.90	$243.90
Purchase #2	$31.48	6.382%	$33.4891	$33.49	$33.50	$33.50
Purchase #3	$133.82	4.824%	$140.2755	$140.28	$140.30	$140.30
Purchase #4	$139.76	13.683%	$158.8834	$158.88	$158.90	$158.90
Purchase #5	$213.97	13.148%	$242.1028	$242.10	$242.10	$242.10
Purchase #6	$18.55	6.635%	$19.7808	$19.78	$19.80	$19.80
Purchase #7	$60.26	12.568%	$67.8335	$67.83	$67.85	$67.80
7 purchase totals =	$820.70		$906.2430	$906.24	$906.35	$906.30