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	$72.83	6.319%	$77.4321	$77.43	$77.45	$77.40
Purchase #2	$36.92	9.514%	$40.4326	$40.43	$40.45	$40.40
Purchase #3	$136.97	11.329%	$152.4873	$152.49	$152.50	$152.50
Purchase #4	$145.26	10.226%	$160.1143	$160.11	$160.10	$160.10
Purchase #5	$188.88	6.231%	$200.6491	$200.65	$200.65	$200.60
Purchase #6	$80.79	11.642%	$90.1956	$90.20	$90.20	$90.20
Purchase #7	$146.89	11.666%	$164.0262	$164.03	$164.05	$164.00
7 purchase totals =	$808.54		$885.3372	$885.34	$885.40	$885.20