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	$225.53	11.187%	$250.76	$250.76	$250.75	$250.80
Purchase #2	$50.73	8.427%	$55.005	$55.01	$55.00	$55.00
Purchase #3	$176.38	7.812%	$190.1588	$190.16	$190.15	$190.20
Purchase #4	$98.33	8.558%	$106.7451	$106.75	$106.75	$106.70
Purchase #5	$35.96	6.649%	$38.351	$38.35	$38.35	$38.40
Purchase #6	$208.76	6.505%	$222.3398	$222.34	$222.35	$222.30
Purchase #7	$47.91	8.553%	$52.0077	$52.01	$52.00	$52.00
7 purchase totals =	$843.60		$915.3674	$915.38	$915.35	$915.40