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	$73.84	4.283%	$77.0026	$77.00	$77.00	$77.00
Purchase #2	$187.33	11.534%	$208.9366	$208.94	$208.95	$208.90
Purchase #3	$63.36	13.756%	$72.0758	$72.08	$72.10	$72.10
Purchase #4	$80.43	12.355%	$90.3671	$90.37	$90.35	$90.40
Purchase #5	$78.37	5.668%	$82.812	$82.81	$82.80	$82.80
Purchase #6	$21.45	5.675%	$22.6673	$22.67	$22.65	$22.70
Purchase #7	$232.28	12.499%	$261.3127	$261.31	$261.30	$261.30
7 purchase totals =	$737.06		$815.1741	$815.18	$815.15	$815.20