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	$14.47	7.301%	$15.5265	$15.53	$15.55	$15.50
Purchase #2	$33.37	5.438%	$35.1847	$35.18	$35.20	$35.20
Purchase #3	$168.34	12.167%	$188.8219	$188.82	$188.80	$188.80
Purchase #4	$111.89	12.158%	$125.4936	$125.49	$125.50	$125.50
Purchase #5	$115.61	6.815%	$123.4888	$123.49	$123.50	$123.50
Purchase #6	$228.63	6.335%	$243.1137	$243.11	$243.10	$243.10
Purchase #7	$63.34	5.318%	$66.7084	$66.71	$66.70	$66.70
7 purchase totals =	$735.65		$798.3376	$798.33	$798.35	$798.30