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	$115.82	13.449%	$131.3966	$131.40	$131.40	$131.40
Purchase #2	$189.59	9.680%	$207.9423	$207.94	$207.95	$207.90
Purchase #3	$101.51	12.512%	$114.2109	$114.21	$114.20	$114.20
Purchase #4	$35.75	4.377%	$37.3148	$37.31	$37.30	$37.30
Purchase #5	$211.73	3.641%	$219.4391	$219.44	$219.45	$219.40
Purchase #6	$96.40	4.207%	$100.4555	$100.46	$100.45	$100.50
Purchase #7	$213.34	6.580%	$227.3778	$227.38	$227.40	$227.40
7 purchase totals =	$964.14		$1,038.1370	$1,038.14	$1,038.15	$1,038.10