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	$33.92	11.139%	$37.6983	$37.70	$37.70	$37.70
Purchase #2	$92.69	4.116%	$96.5051	$96.51	$96.50	$96.50
Purchase #3	$27.93	10.844%	$30.9587	$30.96	$30.95	$31.00
Purchase #4	$125.49	4.725%	$131.4194	$131.42	$131.40	$131.40
Purchase #5	$69.94	12.260%	$78.5146	$78.51	$78.50	$78.50
Purchase #6	$37.61	11.363%	$41.8836	$41.88	$41.90	$41.90
Purchase #7	$217.64	8.819%	$236.8337	$236.83	$236.85	$236.80
7 purchase totals =	$605.22		$653.8134	$653.81	$653.80	$653.80