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	$199.61	11.765%	$223.0941	$223.09	$223.10	$223.10
Purchase #2	$78.68	6.172%	$83.5361	$83.54	$83.55	$83.50
Purchase #3	$190.33	11.133%	$211.5194	$211.52	$211.50	$211.50
Purchase #4	$19.38	8.505%	$21.0283	$21.03	$21.05	$21.00
Purchase #5	$53.73	5.859%	$56.878	$56.88	$56.90	$56.90
Purchase #6	$202.32	7.495%	$217.4839	$217.48	$217.50	$217.50
Purchase #7	$41.52	8.141%	$44.9001	$44.90	$44.90	$44.90
7 purchase totals =	$785.57		$858.4399	$858.44	$858.50	$858.40