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	$122.78	12.128%	$137.6708	$137.67	$137.65	$137.70
Purchase #2	$51.88	4.392%	$54.1586	$54.16	$54.15	$54.20
Purchase #3	$100.82	9.197%	$110.0924	$110.09	$110.10	$110.10
Purchase #4	$234.96	6.497%	$250.2254	$250.23	$250.25	$250.20
Purchase #5	$63.33	12.583%	$71.2988	$71.30	$71.30	$71.30
Purchase #6	$104.86	7.457%	$112.6794	$112.68	$112.70	$112.70
Purchase #7	$141.90	5.797%	$150.1259	$150.13	$150.15	$150.10
7 purchase totals =	$820.53		$886.2513	$886.26	$886.30	$886.30