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	$170.55	12.416%	$191.7255	$191.73	$191.75	$191.70
Purchase #2	$111.96	7.391%	$120.235	$120.24	$120.25	$120.20
Purchase #3	$109.88	9.754%	$120.5977	$120.60	$120.60	$120.60
Purchase #4	$95.81	10.339%	$105.7158	$105.72	$105.70	$105.70
Purchase #5	$111.89	10.550%	$123.6944	$123.69	$123.70	$123.70
Purchase #6	$123.63	13.173%	$139.9158	$139.92	$139.90	$139.90
Purchase #7	$171.84	8.419%	$186.3072	$186.31	$186.30	$186.30
7 purchase totals =	$895.56		$988.1914	$988.21	$988.20	$988.10