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	$85.32	13.503%	$96.8408	$96.84	$96.85	$96.80
Purchase #2	$17.39	5.656%	$18.3736	$18.37	$18.35	$18.40
Purchase #3	$60.82	11.599%	$67.8745	$67.87	$67.85	$67.90
Purchase #4	$137.62	13.458%	$156.1409	$156.14	$156.15	$156.10
Purchase #5	$37.35	11.167%	$41.5209	$41.52	$41.50	$41.50
Purchase #6	$171.54	6.731%	$183.0864	$183.09	$183.10	$183.10
Purchase #7	$76.41	4.865%	$80.1273	$80.13	$80.15	$80.10
7 purchase totals =	$586.45		$643.9644	$643.96	$643.95	$643.90