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	$156.94	11.473%	$174.9457	$174.95	$174.95	$174.90
Purchase #2	$133.88	10.184%	$147.5143	$147.51	$147.50	$147.50
Purchase #3	$93.98	6.780%	$100.3518	$100.35	$100.35	$100.40
Purchase #4	$51.61	7.725%	$55.5969	$55.60	$55.60	$55.60
Purchase #5	$64.88	13.282%	$73.4974	$73.50	$73.50	$73.50
Purchase #6	$227.98	9.713%	$250.1237	$250.12	$250.10	$250.10
Purchase #7	$42.29	13.525%	$48.0097	$48.01	$48.00	$48.00
7 purchase totals =	$771.56		$850.0395	$850.04	$850.00	$850.00