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	$125.66	3.113%	$129.5718	$129.57	$129.55	$129.60
Purchase #2	$42.77	5.625%	$45.1758	$45.18	$45.20	$45.20
Purchase #3	$136.97	11.308%	$152.4586	$152.46	$152.45	$152.50
Purchase #4	$134.39	3.774%	$139.4619	$139.46	$139.45	$139.50
Purchase #5	$95.32	13.693%	$108.3722	$108.37	$108.35	$108.40
Purchase #6	$19.63	3.220%	$20.2621	$20.26	$20.25	$20.30
Purchase #7	$168.97	11.737%	$188.802	$188.80	$188.80	$188.80
7 purchase totals =	$723.71		$784.1044	$784.10	$784.05	$784.30