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	$190.38	6.599%	$202.9432	$202.94	$202.95	$202.90
Purchase #2	$121.52	8.245%	$131.5393	$131.54	$131.55	$131.50
Purchase #3	$151.46	8.573%	$164.4447	$164.44	$164.45	$164.40
Purchase #4	$62.94	13.515%	$71.4463	$71.45	$71.45	$71.40
Purchase #5	$23.25	5.479%	$24.5239	$24.52	$24.50	$24.50
Purchase #6	$86.48	13.640%	$98.2759	$98.28	$98.30	$98.30
Purchase #7	$163.44	13.757%	$185.9244	$185.92	$185.90	$185.90
7 purchase totals =	$799.47		$879.0977	$879.09	$879.10	$878.90