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	$34.90	5.190%	$36.7113	$36.71	$36.70	$36.70
Purchase #2	$146.98	6.142%	$156.0075	$156.01	$156.00	$156.00
Purchase #3	$151.62	12.645%	$170.7923	$170.79	$170.80	$170.80
Purchase #4	$37.74	12.864%	$42.5949	$42.59	$42.60	$42.60
Purchase #5	$48.83	3.618%	$50.5967	$50.60	$50.60	$50.60
Purchase #6	$73.85	11.488%	$82.3339	$82.33	$82.35	$82.30
Purchase #7	$32.60	3.544%	$33.7553	$33.76	$33.75	$33.80
7 purchase totals =	$526.52		$572.7919	$572.79	$572.80	$572.80