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	$94.62	9.790%	$103.8833	$103.88	$103.90	$103.90
Purchase #2	$61.85	11.708%	$69.0914	$69.09	$69.10	$69.10
Purchase #3	$54.36	9.511%	$59.5302	$59.53	$59.55	$59.50
Purchase #4	$64.30	13.433%	$72.9374	$72.94	$72.95	$72.90
Purchase #5	$6.94	3.269%	$7.1669	$7.17	$7.15	$7.20
Purchase #6	$42.27	12.706%	$47.6408	$47.64	$47.65	$47.60
Purchase #7	$196.64	11.593%	$219.4365	$219.44	$219.45	$219.40
7 purchase totals =	$520.98		$579.6865	$579.69	$579.75	$579.60