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	$245.45	7.872%	$264.7718	$264.77	$264.75	$264.80
Purchase #2	$230.39	5.198%	$242.3657	$242.37	$242.35	$242.40
Purchase #3	$155.56	12.400%	$174.8494	$174.85	$174.85	$174.80
Purchase #4	$102.87	8.741%	$111.8619	$111.86	$111.85	$111.90
Purchase #5	$63.71	13.503%	$72.3128	$72.31	$72.30	$72.30
Purchase #6	$186.41	7.715%	$200.7915	$200.79	$200.80	$200.80
Purchase #7	$216.81	3.241%	$223.8368	$223.84	$223.85	$223.80
7 purchase totals =	$1,201.20		$1,290.7899	$1,290.79	$1,290.75	$1,290.80