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	$233.41	9.247%	$254.9934	$254.99	$255.00	$255.00
Purchase #2	$239.68	12.301%	$269.163	$269.16	$269.15	$269.20
Purchase #3	$212.91	13.142%	$240.8906	$240.89	$240.90	$240.90
Purchase #4	$242.61	13.860%	$276.2357	$276.24	$276.25	$276.20
Purchase #5	$91.56	8.795%	$99.6127	$99.61	$99.60	$99.60
Purchase #6	$148.68	9.590%	$162.9384	$162.94	$162.95	$162.90
Purchase #7	$198.89	5.441%	$209.7116	$209.71	$209.70	$209.70
7 purchase totals =	$1,367.74		$1,513.5454	$1,513.54	$1,513.55	$1,513.50