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	$23.84	13.423%	$27.04	$27.04	$27.05	$27.00
Purchase #2	$48.33	12.736%	$54.4853	$54.49	$54.50	$54.50
Purchase #3	$111.33	8.166%	$120.4212	$120.42	$120.40	$120.40
Purchase #4	$42.46	3.375%	$43.893	$43.89	$43.90	$43.90
Purchase #5	$131.98	11.367%	$146.9822	$146.98	$147.00	$147.00
Purchase #6	$98.37	5.178%	$103.4636	$103.46	$103.45	$103.50
Purchase #7	$227.34	13.815%	$258.747	$258.75	$258.75	$258.70
7 purchase totals =	$683.65		$755.0323	$755.03	$755.05	$755.00