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	$156.87	6.212%	$166.6148	$166.61	$166.60	$166.60
Purchase #2	$190.63	11.680%	$212.8956	$212.90	$212.90	$212.90
Purchase #3	$180.88	8.374%	$196.0269	$196.03	$196.05	$196.00
Purchase #4	$93.59	9.451%	$102.4352	$102.44	$102.45	$102.40
Purchase #5	$84.79	5.281%	$89.2678	$89.27	$89.25	$89.30
Purchase #6	$41.30	9.712%	$45.3111	$45.31	$45.30	$45.30
Purchase #7	$168.32	3.391%	$174.0277	$174.03	$174.05	$174.00
7 purchase totals =	$916.38		$986.5791	$986.59	$986.60	$986.50