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	$83.67	7.838%	$90.2281	$90.23	$90.25	$90.20
Purchase #2	$101.43	13.165%	$114.7833	$114.78	$114.80	$114.80
Purchase #3	$101.69	12.468%	$114.3687	$114.37	$114.35	$114.40
Purchase #4	$129.40	9.300%	$141.4342	$141.43	$141.45	$141.40
Purchase #5	$198.29	9.382%	$216.8936	$216.89	$216.90	$216.90
Purchase #6	$92.62	7.295%	$99.3766	$99.38	$99.40	$99.40
Purchase #7	$130.86	10.864%	$145.0766	$145.08	$145.10	$145.10
7 purchase totals =	$837.96		$922.1611	$922.16	$922.25	$922.20