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	$133.93	12.358%	$150.4811	$150.48	$150.50	$150.50
Purchase #2	$29.36	6.342%	$31.222	$31.22	$31.20	$31.20
Purchase #3	$242.37	9.810%	$266.1465	$266.15	$266.15	$266.10
Purchase #4	$61.76	4.468%	$64.5194	$64.52	$64.50	$64.50
Purchase #5	$19.66	7.582%	$21.1506	$21.15	$21.15	$21.20
Purchase #6	$206.61	7.204%	$221.4942	$221.49	$221.50	$221.50
Purchase #7	$68.30	6.175%	$72.5175	$72.52	$72.50	$72.50
7 purchase totals =	$761.99		$827.5313	$827.53	$827.50	$827.50