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	$179.48	13.708%	$204.0831	$204.08	$204.10	$204.10
Purchase #2	$28.81	8.649%	$31.3018	$31.30	$31.30	$31.30
Purchase #3	$85.76	10.334%	$94.6224	$94.62	$94.60	$94.60
Purchase #4	$203.38	3.153%	$209.7926	$209.79	$209.80	$209.80
Purchase #5	$9.35	8.179%	$10.1147	$10.11	$10.10	$10.10
Purchase #6	$55.62	7.670%	$59.8861	$59.89	$59.90	$59.90
Purchase #7	$54.77	5.853%	$57.9757	$57.98	$58.00	$58.00
7 purchase totals =	$617.17		$667.7764	$667.77	$667.80	$667.80