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	$130.84	7.371%	$140.4842	$140.48	$140.50	$140.50
Purchase #2	$6.42	13.663%	$7.2972	$7.30	$7.30	$7.30
Purchase #3	$94.62	6.551%	$100.8186	$100.82	$100.80	$100.80
Purchase #4	$168.95	10.302%	$186.3552	$186.36	$186.35	$186.40
Purchase #5	$67.85	8.293%	$73.4768	$73.48	$73.50	$73.50
Purchase #6	$204.94	9.245%	$223.8867	$223.89	$223.90	$223.90
Purchase #7	$58.92	12.713%	$66.4105	$66.41	$66.40	$66.40
7 purchase totals =	$732.54		$798.7292	$798.74	$798.75	$798.80