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	$56.55	4.492%	$59.0902	$59.09	$59.10	$59.10
Purchase #2	$244.62	11.865%	$273.6442	$273.64	$273.65	$273.60
Purchase #3	$57.93	5.707%	$61.2361	$61.24	$61.25	$61.20
Purchase #4	$93.78	5.858%	$99.2736	$99.27	$99.25	$99.30
Purchase #5	$202.43	9.121%	$220.8936	$220.89	$220.90	$220.90
Purchase #6	$38.84	6.423%	$41.3347	$41.33	$41.35	$41.30
Purchase #7	$246.73	7.422%	$265.0423	$265.04	$265.05	$265.00
7 purchase totals =	$940.88		$1,020.5147	$1,020.50	$1,020.55	$1,020.40