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	$134.45	12.687%	$151.5077	$151.51	$151.50	$151.50
Purchase #2	$170.70	10.614%	$188.8181	$188.82	$188.80	$188.80
Purchase #3	$55.58	7.504%	$59.7507	$59.75	$59.75	$59.80
Purchase #4	$95.90	3.579%	$99.3323	$99.33	$99.35	$99.30
Purchase #5	$6.39	12.300%	$7.176	$7.18	$7.20	$7.20
Purchase #6	$38.93	12.217%	$43.6861	$43.69	$43.70	$43.70
Purchase #7	$53.89	9.848%	$59.1971	$59.20	$59.20	$59.20
7 purchase totals =	$555.84		$609.4680	$609.48	$609.50	$609.50