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	$200.56	7.316%	$215.233	$215.23	$215.25	$215.20
Purchase #2	$90.41	12.380%	$101.6028	$101.60	$101.60	$101.60
Purchase #3	$121.71	4.593%	$127.3001	$127.30	$127.30	$127.30
Purchase #4	$250.74	8.567%	$272.2209	$272.22	$272.20	$272.20
Purchase #5	$40.40	6.850%	$43.1674	$43.17	$43.15	$43.20
Purchase #6	$73.46	12.661%	$82.7608	$82.76	$82.75	$82.80
Purchase #7	$77.77	3.526%	$80.5122	$80.51	$80.50	$80.50
7 purchase totals =	$855.05		$922.7972	$922.79	$922.75	$922.80