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	$42.30	7.492%	$45.4691	$45.47	$45.45	$45.50
Purchase #2	$189.80	4.735%	$198.787	$198.79	$198.80	$198.80
Purchase #3	$38.65	9.580%	$42.3527	$42.35	$42.35	$42.40
Purchase #4	$26.41	4.649%	$27.6378	$27.64	$27.65	$27.60
Purchase #5	$100.54	11.816%	$112.4198	$112.42	$112.40	$112.40
Purchase #6	$199.63	5.729%	$211.0668	$211.07	$211.05	$211.10
Purchase #7	$33.28	13.589%	$37.8024	$37.80	$37.80	$37.80
7 purchase totals =	$630.61		$675.5356	$675.54	$675.50	$675.60