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	$80.46	5.106%	$84.5683	$84.57	$84.55	$84.60
Purchase #2	$152.31	12.382%	$171.169	$171.17	$171.15	$171.20
Purchase #3	$235.50	5.162%	$247.6565	$247.66	$247.65	$247.70
Purchase #4	$92.40	7.814%	$99.6201	$99.62	$99.60	$99.60
Purchase #5	$245.30	10.124%	$270.1342	$270.13	$270.15	$270.10
Purchase #6	$182.74	7.325%	$196.1257	$196.13	$196.15	$196.10
Purchase #7	$101.30	13.834%	$115.3138	$115.31	$115.30	$115.30
7 purchase totals =	$1,090.01		$1,184.5876	$1,184.59	$1,184.55	$1,184.60