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	$74.30	6.284%	$78.969	$78.97	$78.95	$79.00
Purchase #2	$211.78	6.673%	$225.9121	$225.91	$225.90	$225.90
Purchase #3	$237.76	7.225%	$254.9382	$254.94	$254.95	$254.90
Purchase #4	$75.36	3.741%	$78.1792	$78.18	$78.20	$78.20
Purchase #5	$210.79	10.280%	$232.4592	$232.46	$232.45	$232.50
Purchase #6	$95.37	10.869%	$105.7358	$105.74	$105.75	$105.70
Purchase #7	$114.92	7.369%	$123.3885	$123.39	$123.40	$123.40
7 purchase totals =	$1,020.28		$1,099.5820	$1,099.59	$1,099.60	$1,099.60