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	$45.58	8.386%	$49.4023	$49.40	$49.40	$49.40
Purchase #2	$146.47	7.127%	$156.9089	$156.91	$156.90	$156.90
Purchase #3	$119.78	10.214%	$132.0143	$132.01	$132.00	$132.00
Purchase #4	$245.66	5.710%	$259.6872	$259.69	$259.70	$259.70
Purchase #5	$108.69	10.227%	$119.8057	$119.81	$119.80	$119.80
Purchase #6	$148.28	5.771%	$156.8372	$156.84	$156.85	$156.80
Purchase #7	$189.32	3.600%	$196.1355	$196.14	$196.15	$196.10
7 purchase totals =	$1,003.78		$1,070.7911	$1,070.80	$1,070.80	$1,070.70