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	$70.64	11.591%	$78.8279	$78.83	$78.85	$78.80
Purchase #2	$131.93	8.556%	$143.2179	$143.22	$143.20	$143.20
Purchase #3	$126.91	10.736%	$140.5351	$140.54	$140.55	$140.50
Purchase #4	$201.59	12.728%	$227.2484	$227.25	$227.25	$227.20
Purchase #5	$131.42	10.198%	$144.8222	$144.82	$144.80	$144.80
Purchase #6	$102.37	12.790%	$115.4631	$115.46	$115.45	$115.50
Purchase #7	$195.99	10.279%	$216.1358	$216.14	$216.15	$216.10
7 purchase totals =	$960.85		$1,066.2504	$1,066.26	$1,066.25	$1,066.10