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	$153.70	11.524%	$171.4124	$171.41	$171.40	$171.40
Purchase #2	$142.87	3.706%	$148.1648	$148.16	$148.15	$148.20
Purchase #3	$171.25	10.817%	$189.7741	$189.77	$189.75	$189.80
Purchase #4	$136.39	3.147%	$140.6822	$140.68	$140.70	$140.70
Purchase #5	$25.64	9.359%	$28.0396	$28.04	$28.05	$28.00
Purchase #6	$237.98	13.228%	$269.46	$269.46	$269.45	$269.50
Purchase #7	$147.54	11.274%	$164.1737	$164.17	$164.15	$164.20
7 purchase totals =	$1,015.37		$1,111.7068	$1,111.69	$1,111.65	$1,111.80