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	$59.63	9.284%	$65.166	$65.17	$65.15	$65.20
Purchase #2	$167.34	6.646%	$178.4614	$178.46	$178.45	$178.50
Purchase #3	$122.38	4.794%	$128.2469	$128.25	$128.25	$128.20
Purchase #4	$245.33	11.598%	$273.7834	$273.78	$273.80	$273.80
Purchase #5	$13.78	7.257%	$14.78	$14.78	$14.80	$14.80
Purchase #6	$193.45	8.631%	$210.1467	$210.15	$210.15	$210.10
Purchase #7	$122.25	6.578%	$130.2916	$130.29	$130.30	$130.30
7 purchase totals =	$924.16		$1,000.8760	$1,000.88	$1,000.90	$1,000.90