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	$45.29	11.316%	$50.415	$50.42	$50.40	$50.40
Purchase #2	$141.46	10.688%	$156.5792	$156.58	$156.60	$156.60
Purchase #3	$38.48	8.558%	$41.7731	$41.77	$41.75	$41.80
Purchase #4	$104.91	8.584%	$113.9155	$113.92	$113.90	$113.90
Purchase #5	$210.89	3.530%	$218.3344	$218.33	$218.35	$218.30
Purchase #6	$163.79	4.467%	$171.1065	$171.11	$171.10	$171.10
Purchase #7	$142.88	13.729%	$162.496	$162.50	$162.50	$162.50
7 purchase totals =	$847.70		$914.6197	$914.63	$914.60	$914.60