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	$9.47	6.676%	$10.1022	$10.10	$10.10	$10.10
Purchase #2	$135.56	7.803%	$146.1377	$146.14	$146.15	$146.10
Purchase #3	$114.67	9.823%	$125.934	$125.93	$125.95	$125.90
Purchase #4	$67.98	6.325%	$72.2797	$72.28	$72.30	$72.30
Purchase #5	$215.34	7.465%	$231.4151	$231.42	$231.40	$231.40
Purchase #6	$114.61	12.404%	$128.8262	$128.83	$128.85	$128.80
Purchase #7	$35.91	6.172%	$38.1264	$38.13	$38.15	$38.10
7 purchase totals =	$693.54		$752.8213	$752.83	$752.90	$752.70