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	$130.55	3.122%	$134.6258	$134.63	$134.65	$134.60
Purchase #2	$108.69	9.732%	$119.2677	$119.27	$119.25	$119.30
Purchase #3	$199.67	13.126%	$225.8787	$225.88	$225.90	$225.90
Purchase #4	$96.88	8.260%	$104.8823	$104.88	$104.90	$104.90
Purchase #5	$24.82	11.633%	$27.7073	$27.71	$27.70	$27.70
Purchase #6	$244.47	12.607%	$275.2903	$275.29	$275.30	$275.30
Purchase #7	$206.81	13.813%	$235.3767	$235.38	$235.40	$235.40
7 purchase totals =	$1,011.89		$1,123.0288	$1,123.04	$1,123.10	$1,123.10