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	$26.54	9.139%	$28.9655	$28.97	$28.95	$29.00
Purchase #2	$37.99	5.660%	$40.1402	$40.14	$40.15	$40.10
Purchase #3	$94.86	6.122%	$100.6673	$100.67	$100.65	$100.70
Purchase #4	$182.81	8.539%	$198.4201	$198.42	$198.40	$198.40
Purchase #5	$196.50	13.759%	$223.5364	$223.54	$223.55	$223.50
Purchase #6	$84.48	3.144%	$87.1361	$87.14	$87.15	$87.10
Purchase #7	$193.36	11.741%	$216.0624	$216.06	$216.05	$216.10
7 purchase totals =	$816.54		$894.9280	$894.94	$894.90	$894.90