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	$91.38	10.295%	$100.7876	$100.79	$100.80	$100.80
Purchase #2	$176.30	6.516%	$187.7877	$187.79	$187.80	$187.80
Purchase #3	$81.84	13.583%	$92.9563	$92.96	$92.95	$93.00
Purchase #4	$32.93	13.394%	$37.3406	$37.34	$37.35	$37.30
Purchase #5	$239.48	6.206%	$254.3421	$254.34	$254.35	$254.30
Purchase #6	$80.44	6.688%	$85.8198	$85.82	$85.80	$85.80
Purchase #7	$104.35	5.143%	$109.7167	$109.72	$109.70	$109.70
7 purchase totals =	$806.72		$868.7508	$868.76	$868.75	$868.70