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	$169.26	7.857%	$182.5588	$182.56	$182.55	$182.60
Purchase #2	$96.68	6.791%	$103.2455	$103.25	$103.25	$103.20
Purchase #3	$125.76	11.580%	$140.323	$140.32	$140.30	$140.30
Purchase #4	$199.56	3.298%	$206.1415	$206.14	$206.15	$206.10
Purchase #5	$63.87	6.281%	$67.8817	$67.88	$67.90	$67.90
Purchase #6	$40.85	11.298%	$45.4652	$45.47	$45.45	$45.50
Purchase #7	$38.73	6.750%	$41.3443	$41.34	$41.35	$41.30
7 purchase totals =	$734.71		$786.9600	$786.96	$786.95	$786.90