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	$47.31	8.124%	$51.1535	$51.15	$51.15	$51.20
Purchase #2	$141.83	7.801%	$152.8942	$152.89	$152.90	$152.90
Purchase #3	$119.75	4.770%	$125.4621	$125.46	$125.45	$125.50
Purchase #4	$246.32	4.762%	$258.0498	$258.05	$258.05	$258.00
Purchase #5	$154.43	9.750%	$169.4869	$169.49	$169.50	$169.50
Purchase #6	$156.44	8.355%	$169.5106	$169.51	$169.50	$169.50
Purchase #7	$207.82	10.356%	$229.3418	$229.34	$229.35	$229.30
7 purchase totals =	$1,073.90		$1,155.8989	$1,155.89	$1,155.90	$1,155.90