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	$73.54	7.284%	$78.8967	$78.90	$78.90	$78.90
Purchase #2	$159.61	5.332%	$168.1204	$168.12	$168.10	$168.10
Purchase #3	$76.34	11.143%	$84.8466	$84.85	$84.85	$84.80
Purchase #4	$115.33	11.569%	$128.6725	$128.67	$128.65	$128.70
Purchase #5	$242.55	10.790%	$268.7211	$268.72	$268.70	$268.70
Purchase #6	$81.38	10.709%	$90.095	$90.10	$90.10	$90.10
Purchase #7	$25.74	12.731%	$29.017	$29.02	$29.00	$29.00
7 purchase totals =	$774.49		$848.3693	$848.38	$848.30	$848.30