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	$41.88	11.848%	$46.8419	$46.84	$46.85	$46.80
Purchase #2	$96.89	12.558%	$109.0574	$109.06	$109.05	$109.10
Purchase #3	$29.53	7.177%	$31.6494	$31.65	$31.65	$31.60
Purchase #4	$182.82	7.274%	$196.1183	$196.12	$196.10	$196.10
Purchase #5	$127.69	11.488%	$142.359	$142.36	$142.35	$142.40
Purchase #6	$87.98	10.243%	$96.9918	$96.99	$97.00	$97.00
Purchase #7	$43.72	9.836%	$48.0203	$48.02	$48.00	$48.00
7 purchase totals =	$610.51		$671.0381	$671.04	$671.00	$671.00