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	$38.52	7.268%	$41.3196	$41.32	$41.30	$41.30
Purchase #2	$106.56	13.146%	$120.5684	$120.57	$120.55	$120.60
Purchase #3	$177.74	10.609%	$196.5964	$196.60	$196.60	$196.60
Purchase #4	$42.34	4.302%	$44.1615	$44.16	$44.15	$44.20
Purchase #5	$6.67	3.376%	$6.8952	$6.90	$6.90	$6.90
Purchase #6	$149.33	10.423%	$164.8947	$164.89	$164.90	$164.90
Purchase #7	$200.32	6.639%	$213.6192	$213.62	$213.60	$213.60
7 purchase totals =	$721.48		$788.0550	$788.06	$788.00	$788.10