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	$61.83	8.590%	$67.1412	$67.14	$67.15	$67.10
Purchase #2	$153.30	4.703%	$160.5097	$160.51	$160.50	$160.50
Purchase #3	$86.73	3.241%	$89.5409	$89.54	$89.55	$89.50
Purchase #4	$201.89	10.680%	$223.4519	$223.45	$223.45	$223.50
Purchase #5	$138.59	7.752%	$149.3335	$149.33	$149.35	$149.30
Purchase #6	$132.77	12.302%	$149.1034	$149.10	$149.10	$149.10
Purchase #7	$35.69	6.807%	$38.1194	$38.12	$38.10	$38.10
7 purchase totals =	$810.80		$877.2000	$877.19	$877.20	$877.10