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	$120.75	6.321%	$128.3826	$128.38	$128.40	$128.40
Purchase #2	$84.48	11.639%	$94.3126	$94.31	$94.30	$94.30
Purchase #3	$97.63	7.867%	$105.3106	$105.31	$105.30	$105.30
Purchase #4	$208.89	3.659%	$216.5333	$216.53	$216.55	$216.50
Purchase #5	$121.36	5.212%	$127.6853	$127.69	$127.70	$127.70
Purchase #6	$87.47	5.584%	$92.3543	$92.35	$92.35	$92.40
Purchase #7	$75.96	8.407%	$82.346	$82.35	$82.35	$82.30
7 purchase totals =	$796.54		$846.9247	$846.92	$846.95	$846.90