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	$39.49	3.204%	$40.7553	$40.76	$40.75	$40.80
Purchase #2	$210.43	3.605%	$218.016	$218.02	$218.00	$218.00
Purchase #3	$203.47	9.761%	$223.3307	$223.33	$223.35	$223.30
Purchase #4	$141.31	10.330%	$155.9073	$155.91	$155.90	$155.90
Purchase #5	$75.40	3.745%	$78.2237	$78.22	$78.20	$78.20
Purchase #6	$134.97	10.704%	$149.4172	$149.42	$149.40	$149.40
Purchase #7	$49.54	11.526%	$55.25	$55.25	$55.25	$55.30
7 purchase totals =	$854.61		$920.9002	$920.91	$920.85	$920.90