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	$10.78	9.455%	$11.7992	$11.80	$11.80	$11.80
Purchase #2	$202.70	3.732%	$210.2648	$210.26	$210.25	$210.30
Purchase #3	$81.88	5.162%	$86.1066	$86.11	$86.10	$86.10
Purchase #4	$102.59	6.566%	$109.3261	$109.33	$109.35	$109.30
Purchase #5	$209.95	6.627%	$223.8634	$223.86	$223.85	$223.90
Purchase #6	$173.78	10.411%	$191.8722	$191.87	$191.85	$191.90
Purchase #7	$76.73	8.402%	$83.1769	$83.18	$83.20	$83.20
7 purchase totals =	$858.41		$916.4092	$916.41	$916.40	$916.50