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	$37.44	4.445%	$39.1042	$39.10	$39.10	$39.10
Purchase #2	$135.36	7.800%	$145.9181	$145.92	$145.90	$145.90
Purchase #3	$89.97	11.527%	$100.3408	$100.34	$100.35	$100.30
Purchase #4	$91.84	9.592%	$100.6493	$100.65	$100.65	$100.60
Purchase #5	$23.78	9.786%	$26.1071	$26.11	$26.10	$26.10
Purchase #6	$39.40	13.434%	$44.693	$44.69	$44.70	$44.70
Purchase #7	$75.48	4.227%	$78.6705	$78.67	$78.65	$78.70
7 purchase totals =	$493.27		$535.4830	$535.48	$535.45	$535.40