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	$11.30	9.214%	$12.3412	$12.34	$12.35	$12.30
Purchase #2	$72.44	8.204%	$78.383	$78.38	$78.40	$78.40
Purchase #3	$147.36	10.542%	$162.8947	$162.89	$162.90	$162.90
Purchase #4	$204.65	11.835%	$228.8703	$228.87	$228.85	$228.90
Purchase #5	$186.56	8.420%	$202.2684	$202.27	$202.25	$202.30
Purchase #6	$36.53	9.706%	$40.0756	$40.08	$40.10	$40.10
Purchase #7	$42.53	7.318%	$45.6423	$45.64	$45.65	$45.60
7 purchase totals =	$701.37		$770.4755	$770.47	$770.50	$770.50