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	$31.57	6.708%	$33.6877	$33.69	$33.70	$33.70
Purchase #2	$248.44	4.608%	$259.8881	$259.89	$259.90	$259.90
Purchase #3	$42.92	5.800%	$45.4094	$45.41	$45.40	$45.40
Purchase #4	$28.91	9.274%	$31.5911	$31.59	$31.60	$31.60
Purchase #5	$240.63	3.776%	$249.7162	$249.72	$249.70	$249.70
Purchase #6	$91.69	6.728%	$97.8589	$97.86	$97.85	$97.90
Purchase #7	$174.51	8.610%	$189.5353	$189.54	$189.55	$189.50
7 purchase totals =	$858.67		$907.6867	$907.70	$907.70	$907.70