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	$90.26	11.674%	$100.797	$100.80	$100.80	$100.80
Purchase #2	$31.84	10.797%	$35.2778	$35.28	$35.30	$35.30
Purchase #3	$245.57	7.201%	$263.2535	$263.25	$263.25	$263.30
Purchase #4	$79.25	8.485%	$85.9744	$85.97	$85.95	$86.00
Purchase #5	$83.87	13.653%	$95.3208	$95.32	$95.30	$95.30
Purchase #6	$195.46	9.623%	$214.2691	$214.27	$214.25	$214.30
Purchase #7	$110.35	12.118%	$123.7222	$123.72	$123.70	$123.70
7 purchase totals =	$836.60		$918.6148	$918.61	$918.55	$918.70