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	$30.98	9.419%	$33.898	$33.90	$33.90	$33.90
Purchase #2	$144.97	3.650%	$150.2614	$150.26	$150.25	$150.30
Purchase #3	$200.55	11.150%	$222.9113	$222.91	$222.90	$222.90
Purchase #4	$28.42	11.392%	$31.6576	$31.66	$31.65	$31.70
Purchase #5	$189.55	6.334%	$201.5561	$201.56	$201.55	$201.60
Purchase #6	$22.62	10.169%	$24.9202	$24.92	$24.90	$24.90
Purchase #7	$163.89	3.328%	$169.3443	$169.34	$169.35	$169.30
7 purchase totals =	$780.98		$834.5489	$834.55	$834.50	$834.60