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	$117.25	11.799%	$131.0843	$131.08	$131.10	$131.10
Purchase #2	$200.63	10.287%	$221.2688	$221.27	$221.25	$221.30
Purchase #3	$148.88	13.371%	$168.7867	$168.79	$168.80	$168.80
Purchase #4	$213.35	4.288%	$222.4984	$222.50	$222.50	$222.50
Purchase #5	$110.33	10.320%	$121.7161	$121.72	$121.70	$121.70
Purchase #6	$47.32	5.815%	$50.0717	$50.07	$50.05	$50.10
Purchase #7	$218.87	11.812%	$244.7229	$244.72	$244.70	$244.70
7 purchase totals =	$1,056.63		$1,160.1489	$1,160.15	$1,160.10	$1,160.20