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	$83.43	7.290%	$89.512	$89.51	$89.50	$89.50
Purchase #2	$51.89	7.329%	$55.693	$55.69	$55.70	$55.70
Purchase #3	$198.75	9.402%	$217.4365	$217.44	$217.45	$217.40
Purchase #4	$58.47	8.629%	$63.5154	$63.52	$63.50	$63.50
Purchase #5	$69.62	5.355%	$73.3482	$73.35	$73.35	$73.30
Purchase #6	$88.83	8.732%	$96.5866	$96.59	$96.60	$96.60
Purchase #7	$51.79	6.698%	$55.2589	$55.26	$55.25	$55.30
7 purchase totals =	$602.78		$651.3506	$651.36	$651.35	$651.30