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	$128.76	10.661%	$142.4871	$142.49	$142.50	$142.50
Purchase #2	$151.54	8.787%	$164.8558	$164.86	$164.85	$164.90
Purchase #3	$233.55	10.361%	$257.7481	$257.75	$257.75	$257.70
Purchase #4	$171.80	6.865%	$183.5941	$183.59	$183.60	$183.60
Purchase #5	$79.47	13.474%	$90.1778	$90.18	$90.20	$90.20
Purchase #6	$124.59	13.259%	$141.1094	$141.11	$141.10	$141.10
Purchase #7	$38.92	5.736%	$41.1525	$41.15	$41.15	$41.20
7 purchase totals =	$928.63		$1,021.1248	$1,021.13	$1,021.15	$1,021.20