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	$28.61	10.715%	$31.6756	$31.68	$31.70	$31.70
Purchase #2	$249.28	11.729%	$278.5181	$278.52	$278.50	$278.50
Purchase #3	$128.75	6.645%	$137.3054	$137.31	$137.30	$137.30
Purchase #4	$128.93	10.143%	$142.0074	$142.01	$142.00	$142.00
Purchase #5	$197.75	5.196%	$208.0251	$208.03	$208.05	$208.00
Purchase #6	$223.46	8.452%	$242.3468	$242.35	$242.35	$242.30
Purchase #7	$95.39	4.808%	$99.9764	$99.98	$100.00	$100.00
7 purchase totals =	$1,052.17		$1,139.8548	$1,139.88	$1,139.90	$1,139.80