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	$25.82	8.737%	$28.0759	$28.08	$28.10	$28.10
Purchase #2	$146.71	12.654%	$165.2747	$165.27	$165.25	$165.30
Purchase #3	$155.90	4.357%	$162.6926	$162.69	$162.70	$162.70
Purchase #4	$185.34	12.814%	$209.0895	$209.09	$209.10	$209.10
Purchase #5	$15.61	3.178%	$16.1061	$16.11	$16.10	$16.10
Purchase #6	$41.38	3.478%	$42.8192	$42.82	$42.80	$42.80
Purchase #7	$114.69	7.373%	$123.1461	$123.15	$123.15	$123.10
7 purchase totals =	$685.45		$747.2041	$747.21	$747.20	$747.20