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	$41.32	5.293%	$43.5071	$43.51	$43.50	$43.50
Purchase #2	$137.52	10.431%	$151.8647	$151.86	$151.85	$151.90
Purchase #3	$173.55	12.373%	$195.0233	$195.02	$195.00	$195.00
Purchase #4	$250.98	12.466%	$282.2672	$282.27	$282.25	$282.30
Purchase #5	$155.31	10.366%	$171.4094	$171.41	$171.40	$171.40
Purchase #6	$58.46	12.645%	$65.8523	$65.85	$65.85	$65.90
Purchase #7	$165.92	8.760%	$180.4546	$180.45	$180.45	$180.50
7 purchase totals =	$983.06		$1,090.3786	$1,090.37	$1,090.30	$1,090.50