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	$29.69	12.459%	$33.3891	$33.39	$33.40	$33.40
Purchase #2	$80.54	11.419%	$89.7369	$89.74	$89.75	$89.70
Purchase #3	$160.44	8.169%	$173.5463	$173.55	$173.55	$173.50
Purchase #4	$247.38	8.793%	$269.1321	$269.13	$269.15	$269.10
Purchase #5	$182.96	8.656%	$198.797	$198.80	$198.80	$198.80
Purchase #6	$78.90	12.605%	$88.8453	$88.85	$88.85	$88.80
Purchase #7	$213.44	6.516%	$227.3478	$227.35	$227.35	$227.30
7 purchase totals =	$993.35		$1,080.7945	$1,080.81	$1,080.85	$1,080.60