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	$139.88	3.457%	$144.7157	$144.72	$144.70	$144.70
Purchase #2	$98.82	6.494%	$105.2374	$105.24	$105.25	$105.20
Purchase #3	$246.87	11.661%	$275.6575	$275.66	$275.65	$275.70
Purchase #4	$181.31	8.448%	$196.6271	$196.63	$196.65	$196.60
Purchase #5	$177.52	12.289%	$199.3354	$199.34	$199.35	$199.30
Purchase #6	$194.25	6.524%	$206.9229	$206.92	$206.90	$206.90
Purchase #7	$41.82	8.345%	$45.3099	$45.31	$45.30	$45.30
7 purchase totals =	$1,080.47		$1,173.8059	$1,173.82	$1,173.80	$1,173.70