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	$244.43	5.111%	$256.9228	$256.92	$256.90	$256.90
Purchase #2	$136.83	3.300%	$141.3454	$141.35	$141.35	$141.30
Purchase #3	$63.43	6.637%	$67.6398	$67.64	$67.65	$67.60
Purchase #4	$21.61	5.160%	$22.7251	$22.73	$22.75	$22.70
Purchase #5	$59.81	8.518%	$64.9046	$64.90	$64.90	$64.90
Purchase #6	$35.31	8.751%	$38.4	$38.40	$38.40	$38.40
Purchase #7	$34.36	10.662%	$38.0235	$38.02	$38.00	$38.00
7 purchase totals =	$595.78		$629.9612	$629.96	$629.95	$629.80