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	$39.36	7.515%	$42.3179	$42.32	$42.30	$42.30
Purchase #2	$27.85	4.475%	$29.0963	$29.10	$29.10	$29.10
Purchase #3	$188.62	9.812%	$207.1274	$207.13	$207.15	$207.10
Purchase #4	$72.83	8.325%	$78.8931	$78.89	$78.90	$78.90
Purchase #5	$125.81	4.134%	$131.011	$131.01	$131.00	$131.00
Purchase #6	$161.80	7.173%	$173.4059	$173.41	$173.40	$173.40
Purchase #7	$211.51	4.664%	$221.3748	$221.37	$221.35	$221.40
7 purchase totals =	$827.78		$883.2264	$883.23	$883.20	$883.20