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	$82.97	7.437%	$89.1405	$89.14	$89.15	$89.10
Purchase #2	$201.49	5.334%	$212.2375	$212.24	$212.25	$212.20
Purchase #3	$242.39	12.157%	$271.8574	$271.86	$271.85	$271.90
Purchase #4	$76.71	11.434%	$85.481	$85.48	$85.50	$85.50
Purchase #5	$202.91	13.403%	$230.106	$230.11	$230.10	$230.10
Purchase #6	$146.43	3.168%	$151.0689	$151.07	$151.05	$151.10
Purchase #7	$39.66	8.134%	$42.8859	$42.89	$42.90	$42.90
7 purchase totals =	$992.56		$1,082.7772	$1,082.79	$1,082.80	$1,082.80