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	$39.86	10.175%	$43.9158	$43.92	$43.90	$43.90
Purchase #2	$74.93	10.285%	$82.6366	$82.64	$82.65	$82.60
Purchase #3	$166.82	4.499%	$174.3252	$174.33	$174.35	$174.30
Purchase #4	$203.95	13.691%	$231.8728	$231.87	$231.85	$231.90
Purchase #5	$85.66	12.692%	$96.532	$96.53	$96.55	$96.50
Purchase #6	$86.77	3.537%	$89.8391	$89.84	$89.85	$89.80
Purchase #7	$246.56	8.713%	$268.0428	$268.04	$268.05	$268.00
7 purchase totals =	$904.55		$987.1643	$987.17	$987.20	$987.00