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	$108.70	10.441%	$120.0494	$120.05	$120.05	$120.00
Purchase #2	$173.32	8.387%	$187.8563	$187.86	$187.85	$187.90
Purchase #3	$188.30	4.341%	$196.4741	$196.47	$196.45	$196.50
Purchase #4	$23.58	7.665%	$25.3874	$25.39	$25.40	$25.40
Purchase #5	$168.74	10.166%	$185.8941	$185.89	$185.90	$185.90
Purchase #6	$61.31	6.488%	$65.2878	$65.29	$65.30	$65.30
Purchase #7	$153.70	7.629%	$165.4258	$165.43	$165.45	$165.40
7 purchase totals =	$877.65		$946.3749	$946.38	$946.40	$946.40