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	$234.96	3.646%	$243.5266	$243.53	$243.55	$243.50
Purchase #2	$176.84	10.213%	$194.9007	$194.90	$194.90	$194.90
Purchase #3	$49.77	6.166%	$52.8388	$52.84	$52.85	$52.80
Purchase #4	$196.54	8.120%	$212.499	$212.50	$212.50	$212.50
Purchase #5	$102.90	11.790%	$115.0319	$115.03	$115.05	$115.00
Purchase #6	$196.42	6.172%	$208.543	$208.54	$208.55	$208.50
Purchase #7	$49.92	6.812%	$53.3206	$53.32	$53.30	$53.30
7 purchase totals =	$1,007.35		$1,080.6606	$1,080.66	$1,080.70	$1,080.50