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	$187.41	9.466%	$205.1502	$205.15	$205.15	$205.20
Purchase #2	$172.46	4.374%	$180.0034	$180.00	$180.00	$180.00
Purchase #3	$70.63	11.754%	$78.9319	$78.93	$78.95	$78.90
Purchase #4	$42.50	7.798%	$45.8142	$45.81	$45.80	$45.80
Purchase #5	$150.95	8.852%	$164.3121	$164.31	$164.30	$164.30
Purchase #6	$73.67	11.520%	$82.1568	$82.16	$82.15	$82.20
Purchase #7	$71.36	3.447%	$73.8198	$73.82	$73.80	$73.80
7 purchase totals =	$768.98		$830.1884	$830.18	$830.15	$830.20