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	$37.94	6.556%	$40.4273	$40.43	$40.45	$40.40
Purchase #2	$137.86	7.762%	$148.5607	$148.56	$148.55	$148.60
Purchase #3	$202.92	4.489%	$212.0291	$212.03	$212.05	$212.00
Purchase #4	$149.97	4.358%	$156.5057	$156.51	$156.50	$156.50
Purchase #5	$36.59	12.701%	$41.2373	$41.24	$41.25	$41.20
Purchase #6	$77.51	9.799%	$85.1052	$85.11	$85.10	$85.10
Purchase #7	$88.67	12.828%	$100.0446	$100.04	$100.05	$100.00
7 purchase totals =	$731.46		$783.9099	$783.92	$783.95	$783.80