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	$54.51	8.665%	$59.2333	$59.23	$59.25	$59.20
Purchase #2	$182.52	4.158%	$190.1092	$190.11	$190.10	$190.10
Purchase #3	$208.48	6.676%	$222.3981	$222.40	$222.40	$222.40
Purchase #4	$243.63	12.741%	$274.6709	$274.67	$274.65	$274.70
Purchase #5	$99.54	5.334%	$104.8495	$104.85	$104.85	$104.80
Purchase #6	$113.48	4.418%	$118.4935	$118.49	$118.50	$118.50
Purchase #7	$191.61	8.604%	$208.0961	$208.10	$208.10	$208.10
7 purchase totals =	$1,093.77		$1,177.8506	$1,177.85	$1,177.85	$1,177.80