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	$189.77	10.276%	$209.2708	$209.27	$209.25	$209.30
Purchase #2	$115.69	4.841%	$121.2906	$121.29	$121.30	$121.30
Purchase #3	$90.78	9.386%	$99.3006	$99.30	$99.30	$99.30
Purchase #4	$18.63	3.844%	$19.3461	$19.35	$19.35	$19.30
Purchase #5	$70.46	9.175%	$76.9247	$76.92	$76.90	$76.90
Purchase #6	$31.53	11.549%	$35.1714	$35.17	$35.15	$35.20
Purchase #7	$38.56	11.125%	$42.8498	$42.85	$42.85	$42.80
7 purchase totals =	$555.42		$604.1540	$604.15	$604.10	$604.10