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	$241.48	13.447%	$273.9518	$273.95	$273.95	$274.00
Purchase #2	$28.97	4.498%	$30.2731	$30.27	$30.25	$30.30
Purchase #3	$186.60	5.697%	$197.2306	$197.23	$197.25	$197.20
Purchase #4	$36.40	11.736%	$40.6719	$40.67	$40.65	$40.70
Purchase #5	$40.69	4.162%	$42.3835	$42.38	$42.40	$42.40
Purchase #6	$172.94	11.524%	$192.8696	$192.87	$192.85	$192.90
Purchase #7	$77.61	5.830%	$82.1347	$82.13	$82.15	$82.10
7 purchase totals =	$784.69		$859.5152	$859.50	$859.50	$859.60