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	$25.79	7.799%	$27.8014	$27.80	$27.80	$27.80
Purchase #2	$88.42	4.683%	$92.5607	$92.56	$92.55	$92.60
Purchase #3	$82.34	9.448%	$90.1195	$90.12	$90.10	$90.10
Purchase #4	$69.78	11.520%	$77.8187	$77.82	$77.80	$77.80
Purchase #5	$40.70	3.581%	$42.1575	$42.16	$42.15	$42.20
Purchase #6	$130.68	12.768%	$147.3652	$147.37	$147.35	$147.40
Purchase #7	$106.34	3.112%	$109.6493	$109.65	$109.65	$109.60
7 purchase totals =	$544.05		$587.4723	$587.48	$587.40	$587.50