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	$88.96	12.527%	$100.104	$100.10	$100.10	$100.10
Purchase #2	$207.91	7.665%	$223.8463	$223.85	$223.85	$223.80
Purchase #3	$98.49	7.360%	$105.7389	$105.74	$105.75	$105.70
Purchase #4	$147.53	13.812%	$167.9068	$167.91	$167.90	$167.90
Purchase #5	$165.38	8.774%	$179.8904	$179.89	$179.90	$179.90
Purchase #6	$175.81	8.387%	$190.5552	$190.56	$190.55	$190.60
Purchase #7	$31.85	3.405%	$32.9345	$32.93	$32.95	$32.90
7 purchase totals =	$915.93		$1,000.9761	$1,000.98	$1,001.00	$1,000.90