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	$242.64	11.814%	$271.3055	$271.31	$271.30	$271.30
Purchase #2	$149.49	11.649%	$166.9041	$166.90	$166.90	$166.90
Purchase #3	$61.56	10.151%	$67.809	$67.81	$67.80	$67.80
Purchase #4	$120.45	5.678%	$127.2892	$127.29	$127.30	$127.30
Purchase #5	$84.76	8.381%	$91.8637	$91.86	$91.85	$91.90
Purchase #6	$225.41	4.645%	$235.8803	$235.88	$235.90	$235.90
Purchase #7	$64.93	3.672%	$67.3142	$67.31	$67.30	$67.30
7 purchase totals =	$949.24		$1,028.3660	$1,028.36	$1,028.35	$1,028.40