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	$30.28	5.278%	$31.8782	$31.88	$31.90	$31.90
Purchase #2	$169.46	13.794%	$192.8353	$192.84	$192.85	$192.80
Purchase #3	$209.67	6.751%	$223.8248	$223.82	$223.80	$223.80
Purchase #4	$110.25	5.525%	$116.3413	$116.34	$116.35	$116.30
Purchase #5	$206.25	7.104%	$220.902	$220.90	$220.90	$220.90
Purchase #6	$150.86	5.376%	$158.9702	$158.97	$158.95	$159.00
Purchase #7	$137.75	6.466%	$146.6569	$146.66	$146.65	$146.70
7 purchase totals =	$1,014.52		$1,091.4087	$1,091.41	$1,091.40	$1,091.40