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	$171.71	11.600%	$191.6284	$191.63	$191.65	$191.60
Purchase #2	$238.76	13.660%	$271.3746	$271.37	$271.35	$271.40
Purchase #3	$103.66	9.271%	$113.2703	$113.27	$113.25	$113.30
Purchase #4	$77.34	6.505%	$82.371	$82.37	$82.35	$82.40
Purchase #5	$114.51	4.761%	$119.9618	$119.96	$119.95	$120.00
Purchase #6	$223.94	13.109%	$253.2963	$253.30	$253.30	$253.30
Purchase #7	$57.95	3.505%	$59.9811	$59.98	$60.00	$60.00
7 purchase totals =	$987.87		$1,091.8835	$1,091.88	$1,091.85	$1,092.00