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	$7.63	7.604%	$8.2102	$8.21	$8.20	$8.20
Purchase #2	$247.85	6.426%	$263.7768	$263.78	$263.80	$263.80
Purchase #3	$55.85	7.228%	$59.8868	$59.89	$59.90	$59.90
Purchase #4	$243.33	4.177%	$253.4939	$253.49	$253.50	$253.50
Purchase #5	$138.59	5.194%	$145.7884	$145.79	$145.80	$145.80
Purchase #6	$184.75	3.470%	$191.1608	$191.16	$191.15	$191.20
Purchase #7	$120.65	6.223%	$128.158	$128.16	$128.15	$128.20
7 purchase totals =	$998.65		$1,050.4749	$1,050.48	$1,050.50	$1,050.60