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	$6.54	8.651%	$7.1058	$7.11	$7.10	$7.10
Purchase #2	$139.88	7.509%	$150.3836	$150.38	$150.40	$150.40
Purchase #3	$239.26	4.184%	$249.2706	$249.27	$249.25	$249.30
Purchase #4	$36.42	4.220%	$37.9569	$37.96	$37.95	$38.00
Purchase #5	$196.39	13.198%	$222.3096	$222.31	$222.30	$222.30
Purchase #6	$214.47	13.502%	$243.4277	$243.43	$243.45	$243.40
Purchase #7	$24.98	8.644%	$27.1393	$27.14	$27.15	$27.10
7 purchase totals =	$857.94		$937.5935	$937.60	$937.60	$937.60