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	$244.85	6.110%	$259.8103	$259.81	$259.80	$259.80
Purchase #2	$141.29	12.166%	$158.4793	$158.48	$158.50	$158.50
Purchase #3	$164.40	11.317%	$183.0051	$183.01	$183.00	$183.00
Purchase #4	$56.35	9.829%	$61.8886	$61.89	$61.90	$61.90
Purchase #5	$80.43	10.244%	$88.6692	$88.67	$88.65	$88.70
Purchase #6	$247.56	11.196%	$275.2768	$275.28	$275.30	$275.30
Purchase #7	$221.87	9.779%	$243.5667	$243.57	$243.55	$243.60
7 purchase totals =	$1,156.75		$1,270.6960	$1,270.71	$1,270.70	$1,270.80