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	$94.59	9.614%	$103.6839	$103.68	$103.70	$103.70
Purchase #2	$82.30	11.546%	$91.8024	$91.80	$91.80	$91.80
Purchase #3	$19.69	6.676%	$21.0045	$21.00	$21.00	$21.00
Purchase #4	$72.50	4.608%	$75.8408	$75.84	$75.85	$75.80
Purchase #5	$250.89	13.343%	$284.3663	$284.37	$284.35	$284.40
Purchase #6	$87.59	4.322%	$91.3756	$91.38	$91.40	$91.40
Purchase #7	$196.80	11.678%	$219.7823	$219.78	$219.80	$219.80
7 purchase totals =	$804.36		$887.8558	$887.85	$887.90	$887.90