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	$41.36	6.157%	$43.9065	$43.91	$43.90	$43.90
Purchase #2	$128.46	6.630%	$136.9769	$136.98	$137.00	$137.00
Purchase #3	$108.88	8.327%	$117.9464	$117.95	$117.95	$117.90
Purchase #4	$149.29	4.498%	$156.0051	$156.01	$156.00	$156.00
Purchase #5	$79.29	12.540%	$89.233	$89.23	$89.25	$89.20
Purchase #6	$85.94	6.588%	$91.6017	$91.60	$91.60	$91.60
Purchase #7	$122.85	11.562%	$137.0539	$137.05	$137.05	$137.10
7 purchase totals =	$716.07		$772.7235	$772.73	$772.75	$772.70