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	$35.67	6.116%	$37.8516	$37.85	$37.85	$37.90
Purchase #2	$65.27	5.796%	$69.053	$69.05	$69.05	$69.10
Purchase #3	$22.66	12.566%	$25.5075	$25.51	$25.50	$25.50
Purchase #4	$118.86	13.830%	$135.2983	$135.30	$135.30	$135.30
Purchase #5	$40.99	7.150%	$43.9208	$43.92	$43.90	$43.90
Purchase #6	$85.25	5.322%	$89.787	$89.79	$89.80	$89.80
Purchase #7	$179.32	9.753%	$196.8091	$196.81	$196.80	$196.80
7 purchase totals =	$548.02		$598.2273	$598.23	$598.20	$598.30