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	$27.30	13.115%	$30.8804	$30.88	$30.90	$30.90
Purchase #2	$164.86	10.702%	$182.5033	$182.50	$182.50	$182.50
Purchase #3	$145.50	13.408%	$165.0086	$165.01	$165.00	$165.00
Purchase #4	$226.33	9.304%	$247.3877	$247.39	$247.40	$247.40
Purchase #5	$250.56	7.171%	$268.5277	$268.53	$268.55	$268.50
Purchase #6	$203.89	5.680%	$215.471	$215.47	$215.45	$215.50
Purchase #7	$112.87	6.250%	$119.9244	$119.92	$119.90	$119.90
7 purchase totals =	$1,131.31		$1,229.7031	$1,229.70	$1,229.70	$1,229.70