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	$121.50	12.511%	$136.7009	$136.70	$136.70	$136.70
Purchase #2	$215.82	10.268%	$237.9804	$237.98	$238.00	$238.00
Purchase #3	$189.28	3.697%	$196.2777	$196.28	$196.30	$196.30
Purchase #4	$70.37	11.228%	$78.2711	$78.27	$78.25	$78.30
Purchase #5	$110.34	9.600%	$120.9326	$120.93	$120.95	$120.90
Purchase #6	$246.33	11.775%	$275.3354	$275.34	$275.35	$275.30
Purchase #7	$99.68	6.648%	$106.3067	$106.31	$106.30	$106.30
7 purchase totals =	$1,053.32		$1,151.8048	$1,151.81	$1,151.85	$1,151.80