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	$109.99	3.841%	$114.2147	$114.21	$114.20	$114.20
Purchase #2	$188.93	10.848%	$209.4251	$209.43	$209.45	$209.40
Purchase #3	$96.33	3.445%	$99.6486	$99.65	$99.65	$99.60
Purchase #4	$118.85	4.211%	$123.8548	$123.85	$123.85	$123.90
Purchase #5	$95.37	11.204%	$106.0553	$106.06	$106.05	$106.10
Purchase #6	$20.38	3.119%	$21.0157	$21.02	$21.00	$21.00
Purchase #7	$76.85	12.204%	$86.2288	$86.23	$86.25	$86.20
7 purchase totals =	$706.70		$760.4430	$760.45	$760.45	$760.40