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	$111.40	13.651%	$126.6072	$126.61	$126.60	$126.60
Purchase #2	$114.99	5.150%	$120.912	$120.91	$120.90	$120.90
Purchase #3	$28.60	4.470%	$29.8784	$29.88	$29.90	$29.90
Purchase #4	$135.80	5.550%	$143.3369	$143.34	$143.35	$143.30
Purchase #5	$102.79	8.873%	$111.9106	$111.91	$111.90	$111.90
Purchase #6	$67.67	7.529%	$72.7649	$72.76	$72.75	$72.80
Purchase #7	$93.33	7.531%	$100.3587	$100.36	$100.35	$100.40
7 purchase totals =	$654.58		$705.7687	$705.77	$705.75	$705.80