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	$15.57	8.559%	$16.9026	$16.90	$16.90	$16.90
Purchase #2	$162.72	5.268%	$171.2921	$171.29	$171.30	$171.30
Purchase #3	$214.59	6.411%	$228.3474	$228.35	$228.35	$228.30
Purchase #4	$196.73	11.831%	$220.0051	$220.01	$220.00	$220.00
Purchase #5	$176.35	6.119%	$187.1409	$187.14	$187.15	$187.10
Purchase #6	$162.93	7.345%	$174.8972	$174.90	$174.90	$174.90
Purchase #7	$38.62	9.454%	$42.2711	$42.27	$42.25	$42.30
7 purchase totals =	$967.51		$1,040.8564	$1,040.86	$1,040.85	$1,040.80