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	$218.54	10.191%	$240.8114	$240.81	$240.80	$240.80
Purchase #2	$227.67	13.736%	$258.9428	$258.94	$258.95	$258.90
Purchase #3	$67.96	6.292%	$72.236	$72.24	$72.25	$72.20
Purchase #4	$12.96	7.199%	$13.893	$13.89	$13.90	$13.90
Purchase #5	$137.61	6.808%	$146.9785	$146.98	$147.00	$147.00
Purchase #6	$98.65	4.413%	$103.0034	$103.00	$103.00	$103.00
Purchase #7	$7.57	12.627%	$8.5259	$8.53	$8.55	$8.50
7 purchase totals =	$770.96		$844.3910	$844.39	$844.45	$844.30