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	$151.94	4.588%	$158.911	$158.91	$158.90	$158.90
Purchase #2	$245.27	9.230%	$267.9084	$267.91	$267.90	$267.90
Purchase #3	$72.86	8.260%	$78.8782	$78.88	$78.90	$78.90
Purchase #4	$167.29	7.655%	$180.096	$180.10	$180.10	$180.10
Purchase #5	$240.74	5.300%	$253.4992	$253.50	$253.50	$253.50
Purchase #6	$127.96	11.295%	$142.4131	$142.41	$142.40	$142.40
Purchase #7	$212.88	4.844%	$223.1919	$223.19	$223.20	$223.20
7 purchase totals =	$1,218.94		$1,304.8978	$1,304.90	$1,304.90	$1,304.90