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	$240.54	12.258%	$270.0254	$270.03	$270.05	$270.00
Purchase #2	$22.27	9.239%	$24.3275	$24.33	$24.35	$24.30
Purchase #3	$249.89	6.140%	$265.2332	$265.23	$265.25	$265.20
Purchase #4	$232.73	8.330%	$252.1164	$252.12	$252.10	$252.10
Purchase #5	$147.50	12.214%	$165.5157	$165.52	$165.50	$165.50
Purchase #6	$181.79	3.711%	$188.5362	$188.54	$188.55	$188.50
Purchase #7	$56.67	4.707%	$59.3375	$59.34	$59.35	$59.30
7 purchase totals =	$1,131.39		$1,225.0919	$1,225.11	$1,225.15	$1,224.90