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	$47.31	12.741%	$53.3378	$53.34	$53.35	$53.30
Purchase #2	$55.72	8.172%	$60.2734	$60.27	$60.25	$60.30
Purchase #3	$131.46	11.676%	$146.8093	$146.81	$146.80	$146.80
Purchase #4	$98.88	7.587%	$106.382	$106.38	$106.40	$106.40
Purchase #5	$119.65	7.380%	$128.4802	$128.48	$128.50	$128.50
Purchase #6	$225.36	9.409%	$246.5641	$246.56	$246.55	$246.60
Purchase #7	$226.29	4.477%	$236.421	$236.42	$236.40	$236.40
7 purchase totals =	$904.67		$978.2678	$978.26	$978.25	$978.30