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	$176.29	4.131%	$183.5725	$183.57	$183.55	$183.60
Purchase #2	$72.76	12.757%	$82.042	$82.04	$82.05	$82.00
Purchase #3	$125.77	10.805%	$139.3594	$139.36	$139.35	$139.40
Purchase #4	$209.78	13.554%	$238.2136	$238.21	$238.20	$238.20
Purchase #5	$95.30	4.146%	$99.2511	$99.25	$99.25	$99.30
Purchase #6	$209.79	4.573%	$219.3837	$219.38	$219.40	$219.40
Purchase #7	$37.85	10.595%	$41.8602	$41.86	$41.85	$41.90
7 purchase totals =	$927.54		$1,003.6825	$1,003.67	$1,003.65	$1,003.80