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	$71.92	8.841%	$78.2784	$78.28	$78.30	$78.30
Purchase #2	$231.96	9.826%	$254.7524	$254.75	$254.75	$254.80
Purchase #3	$147.39	10.419%	$162.7466	$162.75	$162.75	$162.70
Purchase #4	$31.92	12.437%	$35.8899	$35.89	$35.90	$35.90
Purchase #5	$41.32	4.844%	$43.3215	$43.32	$43.30	$43.30
Purchase #6	$20.40	13.471%	$23.1481	$23.15	$23.15	$23.10
Purchase #7	$179.37	4.195%	$186.8946	$186.89	$186.90	$186.90
7 purchase totals =	$724.28		$785.0315	$785.03	$785.05	$785.00