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	$68.35	7.120%	$73.2165	$73.22	$73.20	$73.20
Purchase #2	$241.89	13.460%	$274.4484	$274.45	$274.45	$274.40
Purchase #3	$63.36	13.459%	$71.8876	$71.89	$71.90	$71.90
Purchase #4	$20.87	7.730%	$22.4833	$22.48	$22.50	$22.50
Purchase #5	$36.71	13.605%	$41.7044	$41.70	$41.70	$41.70
Purchase #6	$99.88	5.491%	$105.3644	$105.36	$105.35	$105.40
Purchase #7	$234.42	12.752%	$264.3132	$264.31	$264.30	$264.30
7 purchase totals =	$765.48		$853.4178	$853.41	$853.40	$853.40