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	$176.66	12.360%	$198.4952	$198.50	$198.50	$198.50
Purchase #2	$18.96	6.380%	$20.1696	$20.17	$20.15	$20.20
Purchase #3	$84.80	12.582%	$95.4695	$95.47	$95.45	$95.50
Purchase #4	$64.25	13.353%	$72.8293	$72.83	$72.85	$72.80
Purchase #5	$67.45	9.171%	$73.6358	$73.64	$73.65	$73.60
Purchase #6	$47.90	7.646%	$51.5624	$51.56	$51.55	$51.60
Purchase #7	$58.55	8.582%	$63.5748	$63.57	$63.55	$63.60
7 purchase totals =	$518.57		$575.7366	$575.74	$575.70	$575.80