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	$48.70	12.654%	$54.8625	$54.86	$54.85	$54.90
Purchase #2	$66.79	7.485%	$71.7892	$71.79	$71.80	$71.80
Purchase #3	$209.37	11.282%	$232.9911	$232.99	$233.00	$233.00
Purchase #4	$126.56	10.261%	$139.5463	$139.55	$139.55	$139.50
Purchase #5	$43.60	5.168%	$45.8532	$45.85	$45.85	$45.90
Purchase #6	$245.87	6.427%	$261.6721	$261.67	$261.65	$261.70
Purchase #7	$187.41	11.335%	$208.6529	$208.65	$208.65	$208.70
7 purchase totals =	$928.30		$1,015.3673	$1,015.36	$1,015.35	$1,015.50