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	$5.50	8.150%	$5.9483	$5.95	$5.95	$5.90
Purchase #2	$59.57	13.499%	$67.6114	$67.61	$67.60	$67.60
Purchase #3	$42.31	3.126%	$43.6326	$43.63	$43.65	$43.60
Purchase #4	$131.81	8.427%	$142.9176	$142.92	$142.90	$142.90
Purchase #5	$90.94	9.842%	$99.8903	$99.89	$99.90	$99.90
Purchase #6	$118.33	5.609%	$124.9671	$124.97	$124.95	$125.00
Purchase #7	$85.52	6.323%	$90.9274	$90.93	$90.95	$90.90
7 purchase totals =	$533.98		$575.8947	$575.90	$575.90	$575.80