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	$171.82	10.138%	$189.2391	$189.24	$189.25	$189.20
Purchase #2	$54.48	11.239%	$60.603	$60.60	$60.60	$60.60
Purchase #3	$71.81	13.294%	$81.3564	$81.36	$81.35	$81.40
Purchase #4	$95.77	3.180%	$98.8155	$98.82	$98.80	$98.80
Purchase #5	$37.66	9.715%	$41.3187	$41.32	$41.30	$41.30
Purchase #6	$123.46	13.834%	$140.5395	$140.54	$140.55	$140.50
Purchase #7	$142.89	8.166%	$154.5584	$154.56	$154.55	$154.60
7 purchase totals =	$697.89		$766.4306	$766.44	$766.40	$766.40