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	$102.47	12.131%	$114.9006	$114.90	$114.90	$114.90
Purchase #2	$84.84	7.549%	$91.2446	$91.24	$91.25	$91.20
Purchase #3	$129.67	12.325%	$145.6518	$145.65	$145.65	$145.70
Purchase #4	$123.82	10.609%	$136.9561	$136.96	$136.95	$137.00
Purchase #5	$245.73	7.565%	$264.3195	$264.32	$264.30	$264.30
Purchase #6	$83.69	6.257%	$88.9265	$88.93	$88.95	$88.90
Purchase #7	$65.56	7.672%	$70.5898	$70.59	$70.60	$70.60
7 purchase totals =	$835.78		$912.5889	$912.59	$912.60	$912.60