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	$113.89	6.226%	$120.9808	$120.98	$121.00	$121.00
Purchase #2	$58.39	7.787%	$62.9368	$62.94	$62.95	$62.90
Purchase #3	$35.33	11.171%	$39.2767	$39.28	$39.30	$39.30
Purchase #4	$39.84	9.202%	$43.5061	$43.51	$43.50	$43.50
Purchase #5	$197.57	10.813%	$218.9332	$218.93	$218.95	$218.90
Purchase #6	$71.65	6.342%	$76.194	$76.19	$76.20	$76.20
Purchase #7	$81.84	9.832%	$89.8865	$89.89	$89.90	$89.90
7 purchase totals =	$598.51		$651.7141	$651.72	$651.80	$651.70