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	$245.43	10.202%	$270.4688	$270.47	$270.45	$270.50
Purchase #2	$224.96	8.123%	$243.2335	$243.23	$243.25	$243.20
Purchase #3	$197.69	12.823%	$223.0398	$223.04	$223.05	$223.00
Purchase #4	$21.33	3.618%	$22.1017	$22.10	$22.10	$22.10
Purchase #5	$104.79	6.812%	$111.9283	$111.93	$111.95	$111.90
Purchase #6	$14.91	8.349%	$16.1548	$16.15	$16.15	$16.20
Purchase #7	$175.27	13.806%	$199.4678	$199.47	$199.45	$199.50
7 purchase totals =	$984.38		$1,086.3947	$1,086.39	$1,086.40	$1,086.40