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	$135.86	7.850%	$146.525	$146.53	$146.55	$146.50
Purchase #2	$242.65	9.303%	$265.2237	$265.22	$265.20	$265.20
Purchase #3	$94.79	4.776%	$99.3172	$99.32	$99.30	$99.30
Purchase #4	$223.72	3.454%	$231.4473	$231.45	$231.45	$231.40
Purchase #5	$81.82	13.123%	$92.5572	$92.56	$92.55	$92.60
Purchase #6	$187.44	5.202%	$197.1906	$197.19	$197.20	$197.20
Purchase #7	$45.30	6.559%	$48.2712	$48.27	$48.25	$48.30
7 purchase totals =	$1,011.58		$1,080.5322	$1,080.54	$1,080.50	$1,080.50