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	$98.37	7.275%	$105.5264	$105.53	$105.55	$105.50
Purchase #2	$25.30	12.441%	$28.4476	$28.45	$28.45	$28.40
Purchase #3	$199.36	4.802%	$208.9333	$208.93	$208.95	$208.90
Purchase #4	$115.97	6.677%	$123.7133	$123.71	$123.70	$123.70
Purchase #5	$149.53	7.612%	$160.9122	$160.91	$160.90	$160.90
Purchase #6	$145.56	6.811%	$155.4741	$155.47	$155.45	$155.50
Purchase #7	$47.58	9.253%	$51.9826	$51.98	$52.00	$52.00
7 purchase totals =	$781.67		$834.9895	$834.98	$835.00	$834.90