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	$18.80	5.866%	$19.9028	$19.90	$19.90	$19.90
Purchase #2	$54.73	3.475%	$56.6319	$56.63	$56.65	$56.60
Purchase #3	$39.40	6.216%	$41.8491	$41.85	$41.85	$41.80
Purchase #4	$37.47	6.386%	$39.8628	$39.86	$39.85	$39.90
Purchase #5	$53.33	11.624%	$59.5291	$59.53	$59.55	$59.50
Purchase #6	$191.88	7.457%	$206.1885	$206.19	$206.20	$206.20
Purchase #7	$107.78	10.497%	$119.0937	$119.09	$119.10	$119.10
7 purchase totals =	$503.39		$543.0579	$543.05	$543.10	$543.00