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	$213.92	4.750%	$224.0812	$224.08	$224.10	$224.10
Purchase #2	$77.55	6.650%	$82.7071	$82.71	$82.70	$82.70
Purchase #3	$244.27	12.146%	$273.939	$273.94	$273.95	$273.90
Purchase #4	$81.31	10.645%	$89.9654	$89.97	$89.95	$90.00
Purchase #5	$36.43	6.519%	$38.8049	$38.80	$38.80	$38.80
Purchase #6	$56.56	12.462%	$63.6085	$63.61	$63.60	$63.60
Purchase #7	$41.26	11.361%	$45.9475	$45.95	$45.95	$45.90
7 purchase totals =	$751.30		$819.0536	$819.06	$819.05	$819.00