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	$13.84	11.173%	$15.3863	$15.39	$15.40	$15.40
Purchase #2	$67.89	4.618%	$71.0252	$71.03	$71.05	$71.00
Purchase #3	$12.73	10.796%	$14.1043	$14.10	$14.10	$14.10
Purchase #4	$167.64	12.468%	$188.5414	$188.54	$188.55	$188.50
Purchase #5	$101.54	7.484%	$109.1393	$109.14	$109.15	$109.10
Purchase #6	$114.56	4.589%	$119.8172	$119.82	$119.80	$119.80
Purchase #7	$219.33	6.347%	$233.2509	$233.25	$233.25	$233.30
7 purchase totals =	$697.53		$751.2646	$751.27	$751.30	$751.20