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	$55.33	6.349%	$58.8429	$58.84	$58.85	$58.80
Purchase #2	$229.38	7.529%	$246.65	$246.65	$246.65	$246.70
Purchase #3	$97.73	13.648%	$111.0682	$111.07	$111.05	$111.10
Purchase #4	$39.40	10.390%	$43.4937	$43.49	$43.50	$43.50
Purchase #5	$155.34	8.673%	$168.8126	$168.81	$168.80	$168.80
Purchase #6	$24.94	11.209%	$27.7355	$27.74	$27.75	$27.70
Purchase #7	$168.47	10.336%	$185.8831	$185.88	$185.90	$185.90
7 purchase totals =	$770.59		$842.4860	$842.48	$842.50	$842.50