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	$184.45	6.678%	$196.7676	$196.77	$196.75	$196.80
Purchase #2	$77.88	5.732%	$82.3441	$82.34	$82.35	$82.30
Purchase #3	$219.90	3.138%	$226.8005	$226.80	$226.80	$226.80
Purchase #4	$93.31	3.775%	$96.8325	$96.83	$96.85	$96.80
Purchase #5	$191.46	3.367%	$197.9065	$197.91	$197.90	$197.90
Purchase #6	$213.38	8.506%	$231.5301	$231.53	$231.55	$231.50
Purchase #7	$60.63	11.372%	$67.5248	$67.52	$67.50	$67.50
7 purchase totals =	$1,041.01		$1,099.7061	$1,099.70	$1,099.70	$1,099.60