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	$89.80	12.146%	$100.7071	$100.71	$100.70	$100.70
Purchase #2	$86.63	3.556%	$89.7106	$89.71	$89.70	$89.70
Purchase #3	$213.96	13.361%	$242.5472	$242.55	$242.55	$242.50
Purchase #4	$125.91	10.602%	$139.259	$139.26	$139.25	$139.30
Purchase #5	$89.46	5.232%	$94.1405	$94.14	$94.15	$94.10
Purchase #6	$32.37	13.280%	$36.6687	$36.67	$36.65	$36.70
Purchase #7	$26.96	8.676%	$29.299	$29.30	$29.30	$29.30
7 purchase totals =	$665.09		$732.3321	$732.34	$732.30	$732.30