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	$96.61	3.491%	$99.9827	$99.98	$100.00	$100.00
Purchase #2	$191.91	8.718%	$208.6407	$208.64	$208.65	$208.60
Purchase #3	$220.33	4.254%	$229.7028	$229.70	$229.70	$229.70
Purchase #4	$38.83	12.354%	$43.6271	$43.63	$43.65	$43.60
Purchase #5	$83.60	7.143%	$89.5715	$89.57	$89.55	$89.60
Purchase #6	$76.36	13.373%	$86.5716	$86.57	$86.55	$86.60
Purchase #7	$94.96	8.776%	$103.2937	$103.29	$103.30	$103.30
7 purchase totals =	$802.60		$861.3901	$861.38	$861.40	$861.40