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	$181.25	5.595%	$191.3909	$191.39	$191.40	$191.40
Purchase #2	$104.47	7.755%	$112.5716	$112.57	$112.55	$112.60
Purchase #3	$160.82	7.766%	$173.3093	$173.31	$173.30	$173.30
Purchase #4	$36.76	12.424%	$41.3271	$41.33	$41.35	$41.30
Purchase #5	$113.47	6.219%	$120.5267	$120.53	$120.55	$120.50
Purchase #6	$27.44	9.784%	$30.1247	$30.12	$30.10	$30.10
Purchase #7	$100.79	10.837%	$111.7126	$111.71	$111.70	$111.70
7 purchase totals =	$725.00		$780.9629	$780.96	$780.95	$780.90