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	$99.85	9.438%	$109.2738	$109.27	$109.25	$109.30
Purchase #2	$56.64	11.811%	$63.3298	$63.33	$63.35	$63.30
Purchase #3	$28.59	12.528%	$32.1718	$32.17	$32.15	$32.20
Purchase #4	$41.82	13.437%	$47.4394	$47.44	$47.45	$47.40
Purchase #5	$199.31	11.583%	$222.3961	$222.40	$222.40	$222.40
Purchase #6	$50.44	11.703%	$56.343	$56.34	$56.35	$56.30
Purchase #7	$82.52	8.257%	$89.3337	$89.33	$89.35	$89.30
7 purchase totals =	$559.17		$620.2876	$620.28	$620.30	$620.20