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	$137.67	6.590%	$146.7425	$146.74	$146.75	$146.70
Purchase #2	$242.85	12.447%	$273.0775	$273.08	$273.10	$273.10
Purchase #3	$89.35	12.731%	$100.7251	$100.73	$100.75	$100.70
Purchase #4	$141.78	4.354%	$147.9531	$147.95	$147.95	$148.00
Purchase #5	$193.25	10.503%	$213.547	$213.55	$213.55	$213.50
Purchase #6	$30.85	4.246%	$32.1599	$32.16	$32.15	$32.20
Purchase #7	$179.69	3.379%	$185.7617	$185.76	$185.75	$185.80
7 purchase totals =	$1,015.44		$1,099.9668	$1,099.97	$1,100.00	$1,100.00