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	$182.53	11.708%	$203.9006	$203.90	$203.90	$203.90
Purchase #2	$83.64	12.752%	$94.3058	$94.31	$94.30	$94.30
Purchase #3	$219.78	8.394%	$238.2283	$238.23	$238.25	$238.20
Purchase #4	$11.74	5.134%	$12.3427	$12.34	$12.35	$12.30
Purchase #5	$90.46	6.454%	$96.2983	$96.30	$96.30	$96.30
Purchase #6	$62.83	8.121%	$67.9324	$67.93	$67.95	$67.90
Purchase #7	$146.80	13.349%	$166.3963	$166.40	$166.40	$166.40
7 purchase totals =	$797.78		$879.4044	$879.41	$879.45	$879.30