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	$87.99	13.120%	$99.5343	$99.53	$99.55	$99.50
Purchase #2	$66.25	7.392%	$71.1472	$71.15	$71.15	$71.10
Purchase #3	$82.35	9.528%	$90.1963	$90.20	$90.20	$90.20
Purchase #4	$5.48	12.761%	$6.1793	$6.18	$6.20	$6.20
Purchase #5	$143.55	6.158%	$152.3898	$152.39	$152.40	$152.40
Purchase #6	$175.27	7.811%	$188.9603	$188.96	$188.95	$189.00
Purchase #7	$31.84	8.207%	$34.4531	$34.45	$34.45	$34.50
7 purchase totals =	$592.73		$642.8603	$642.86	$642.90	$642.90