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	$159.70	12.108%	$179.0365	$179.04	$179.05	$179.00
Purchase #2	$35.25	5.138%	$37.0611	$37.06	$37.05	$37.10
Purchase #3	$183.48	11.577%	$204.7215	$204.72	$204.70	$204.70
Purchase #4	$119.45	3.705%	$123.8756	$123.88	$123.90	$123.90
Purchase #5	$72.58	10.380%	$80.1138	$80.11	$80.10	$80.10
Purchase #6	$121.52	6.873%	$129.8721	$129.87	$129.85	$129.90
Purchase #7	$32.97	13.617%	$37.4595	$37.46	$37.45	$37.50
7 purchase totals =	$724.95		$792.1401	$792.14	$792.10	$792.20