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	$69.50	5.279%	$73.1689	$73.17	$73.15	$73.20
Purchase #2	$72.84	7.843%	$78.5528	$78.55	$78.55	$78.60
Purchase #3	$209.42	8.517%	$227.2563	$227.26	$227.25	$227.30
Purchase #4	$89.74	13.492%	$101.8477	$101.85	$101.85	$101.80
Purchase #5	$108.75	4.691%	$113.8515	$113.85	$113.85	$113.90
Purchase #6	$20.30	7.767%	$21.8767	$21.88	$21.90	$21.90
Purchase #7	$102.33	13.474%	$116.1179	$116.12	$116.10	$116.10
7 purchase totals =	$672.88		$732.6718	$732.68	$732.65	$732.80