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	$171.42	8.442%	$185.8913	$185.89	$185.90	$185.90
Purchase #2	$247.46	6.460%	$263.4459	$263.45	$263.45	$263.40
Purchase #3	$39.80	10.254%	$43.8811	$43.88	$43.90	$43.90
Purchase #4	$67.54	7.685%	$72.7304	$72.73	$72.75	$72.70
Purchase #5	$116.97	3.825%	$121.4441	$121.44	$121.45	$121.40
Purchase #6	$204.37	6.396%	$217.4415	$217.44	$217.45	$217.40
Purchase #7	$64.35	10.625%	$71.1872	$71.19	$71.20	$71.20
7 purchase totals =	$911.91		$976.0215	$976.02	$976.10	$975.90