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	$99.50	10.533%	$109.9803	$109.98	$110.00	$110.00
Purchase #2	$145.86	9.812%	$160.1718	$160.17	$160.15	$160.20
Purchase #3	$184.39	13.314%	$208.9397	$208.94	$208.95	$208.90
Purchase #4	$29.89	3.166%	$30.8363	$30.84	$30.85	$30.80
Purchase #5	$97.49	12.408%	$109.5866	$109.59	$109.60	$109.60
Purchase #6	$88.55	12.719%	$99.8127	$99.81	$99.80	$99.80
Purchase #7	$45.38	13.670%	$51.5834	$51.58	$51.60	$51.60
7 purchase totals =	$691.06		$770.9108	$770.91	$770.95	$770.90