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	$137.52	9.285%	$150.2887	$150.29	$150.30	$150.30
Purchase #2	$99.97	6.118%	$106.0862	$106.09	$106.10	$106.10
Purchase #3	$141.59	10.330%	$156.2162	$156.22	$156.20	$156.20
Purchase #4	$158.75	6.434%	$168.964	$168.96	$168.95	$169.00
Purchase #5	$136.46	7.142%	$146.206	$146.21	$146.20	$146.20
Purchase #6	$59.59	12.315%	$66.9285	$66.93	$66.95	$66.90
Purchase #7	$124.44	13.466%	$141.1971	$141.20	$141.20	$141.20
7 purchase totals =	$858.32		$935.8867	$935.90	$935.90	$935.90