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	$120.54	10.444%	$133.1292	$133.13	$133.15	$133.10
Purchase #2	$66.63	9.808%	$73.1651	$73.17	$73.15	$73.20
Purchase #3	$56.94	5.186%	$59.8929	$59.89	$59.90	$59.90
Purchase #4	$118.62	5.856%	$125.5664	$125.57	$125.55	$125.60
Purchase #5	$165.55	10.124%	$182.3103	$182.31	$182.30	$182.30
Purchase #6	$106.42	5.279%	$112.0379	$112.04	$112.05	$112.00
Purchase #7	$117.76	4.710%	$123.3065	$123.31	$123.30	$123.30
7 purchase totals =	$752.46		$809.4083	$809.42	$809.40	$809.40