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	$87.48	13.340%	$99.1498	$99.15	$99.15	$99.10
Purchase #2	$86.25	8.180%	$93.3053	$93.31	$93.30	$93.30
Purchase #3	$46.91	7.234%	$50.3035	$50.30	$50.30	$50.30
Purchase #4	$199.68	9.819%	$219.2866	$219.29	$219.30	$219.30
Purchase #5	$179.81	10.468%	$198.6325	$198.63	$198.65	$198.60
Purchase #6	$209.47	6.867%	$223.8543	$223.85	$223.85	$223.90
Purchase #7	$118.53	11.619%	$132.302	$132.30	$132.30	$132.30
7 purchase totals =	$928.13		$1,016.8340	$1,016.83	$1,016.85	$1,016.80