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	$27.28	4.790%	$28.5867	$28.59	$28.60	$28.60
Purchase #2	$111.27	8.245%	$120.4442	$120.44	$120.45	$120.40
Purchase #3	$200.40	6.782%	$213.9911	$213.99	$214.00	$214.00
Purchase #4	$73.63	12.175%	$82.5945	$82.59	$82.60	$82.60
Purchase #5	$179.94	11.155%	$200.0123	$200.01	$200.00	$200.00
Purchase #6	$215.56	9.490%	$236.0166	$236.02	$236.00	$236.00
Purchase #7	$120.54	8.583%	$130.8859	$130.89	$130.90	$130.90
7 purchase totals =	$928.62		$1,012.5313	$1,012.53	$1,012.55	$1,012.50