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	$231.36	8.397%	$250.7873	$250.79	$250.80	$250.80
Purchase #2	$130.90	13.457%	$148.5152	$148.52	$148.50	$148.50
Purchase #3	$201.50	6.476%	$214.5491	$214.55	$214.55	$214.50
Purchase #4	$243.93	8.564%	$264.8202	$264.82	$264.80	$264.80
Purchase #5	$175.44	11.470%	$195.563	$195.56	$195.55	$195.60
Purchase #6	$187.45	4.803%	$196.4532	$196.45	$196.45	$196.50
Purchase #7	$18.85	13.690%	$21.4306	$21.43	$21.45	$21.40
7 purchase totals =	$1,189.43		$1,292.1186	$1,292.12	$1,292.10	$1,292.10