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	$123.88	4.168%	$129.0433	$129.04	$129.05	$129.00
Purchase #2	$64.86	11.539%	$72.3442	$72.34	$72.35	$72.30
Purchase #3	$114.91	3.627%	$119.0778	$119.08	$119.10	$119.10
Purchase #4	$188.85	13.261%	$213.8934	$213.89	$213.90	$213.90
Purchase #5	$85.70	11.503%	$95.5581	$95.56	$95.55	$95.60
Purchase #6	$64.40	4.548%	$67.3289	$67.33	$67.35	$67.30
Purchase #7	$86.86	4.212%	$90.5185	$90.52	$90.50	$90.50
7 purchase totals =	$729.46		$787.7642	$787.76	$787.80	$787.70