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	$174.33	9.580%	$191.0308	$191.03	$191.05	$191.00
Purchase #2	$106.79	10.388%	$117.8833	$117.88	$117.90	$117.90
Purchase #3	$108.33	7.514%	$116.4699	$116.47	$116.45	$116.50
Purchase #4	$150.50	12.619%	$169.4916	$169.49	$169.50	$169.50
Purchase #5	$18.49	8.229%	$20.0115	$20.01	$20.00	$20.00
Purchase #6	$236.54	9.242%	$258.401	$258.40	$258.40	$258.40
Purchase #7	$54.86	12.811%	$61.8881	$61.89	$61.90	$61.90
7 purchase totals =	$849.84		$935.1762	$935.17	$935.20	$935.20