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	$11.77	10.689%	$13.0281	$13.03	$13.05	$13.00
Purchase #2	$145.25	9.810%	$159.499	$159.50	$159.50	$159.50
Purchase #3	$245.59	12.231%	$275.6281	$275.63	$275.65	$275.60
Purchase #4	$227.31	5.811%	$240.519	$240.52	$240.50	$240.50
Purchase #5	$54.35	9.128%	$59.3111	$59.31	$59.30	$59.30
Purchase #6	$81.38	3.543%	$84.2633	$84.26	$84.25	$84.30
Purchase #7	$166.69	3.137%	$171.9191	$171.92	$171.90	$171.90
7 purchase totals =	$932.34		$1,004.1677	$1,004.17	$1,004.15	$1,004.10