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	$172.61	8.282%	$186.9056	$186.91	$186.90	$186.90
Purchase #2	$18.90	8.343%	$20.4768	$20.48	$20.50	$20.50
Purchase #3	$153.40	10.396%	$169.3475	$169.35	$169.35	$169.30
Purchase #4	$203.72	9.152%	$222.3645	$222.36	$222.35	$222.40
Purchase #5	$63.26	10.558%	$69.939	$69.94	$69.95	$69.90
Purchase #6	$85.85	3.634%	$88.9698	$88.97	$88.95	$89.00
Purchase #7	$41.46	3.471%	$42.8991	$42.90	$42.90	$42.90
7 purchase totals =	$739.20		$800.9023	$800.91	$800.90	$800.90