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	$122.33	7.378%	$131.3555	$131.36	$131.35	$131.40
Purchase #2	$79.70	8.178%	$86.2179	$86.22	$86.20	$86.20
Purchase #3	$151.25	3.638%	$156.7525	$156.75	$156.75	$156.80
Purchase #4	$192.43	9.197%	$210.1278	$210.13	$210.15	$210.10
Purchase #5	$100.35	3.385%	$103.7468	$103.75	$103.75	$103.70
Purchase #6	$198.80	12.406%	$223.4631	$223.46	$223.45	$223.50
Purchase #7	$163.83	3.427%	$169.4445	$169.44	$169.45	$169.40
7 purchase totals =	$1,008.69		$1,081.1081	$1,081.11	$1,081.10	$1,081.10