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	$13.79	6.342%	$14.6646	$14.66	$14.65	$14.70
Purchase #2	$57.51	11.694%	$64.2352	$64.24	$64.25	$64.20
Purchase #3	$145.52	11.611%	$162.4163	$162.42	$162.40	$162.40
Purchase #4	$234.89	6.781%	$250.8179	$250.82	$250.80	$250.80
Purchase #5	$41.31	9.267%	$45.1382	$45.14	$45.15	$45.10
Purchase #6	$81.68	10.116%	$89.9427	$89.94	$89.95	$89.90
Purchase #7	$35.37	12.279%	$39.7131	$39.71	$39.70	$39.70
7 purchase totals =	$610.07		$666.9280	$666.93	$666.90	$666.80