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	$232.85	4.473%	$243.2654	$243.27	$243.25	$243.30
Purchase #2	$138.98	8.812%	$151.2269	$151.23	$151.25	$151.20
Purchase #3	$104.87	5.581%	$110.7228	$110.72	$110.70	$110.70
Purchase #4	$204.26	5.653%	$215.8068	$215.81	$215.80	$215.80
Purchase #5	$100.55	5.285%	$105.8641	$105.86	$105.85	$105.90
Purchase #6	$104.76	8.227%	$113.3786	$113.38	$113.40	$113.40
Purchase #7	$138.96	8.477%	$150.7396	$150.74	$150.75	$150.70
7 purchase totals =	$1,025.23		$1,091.0042	$1,091.01	$1,091.00	$1,091.00