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	$63.28	12.751%	$71.3488	$71.35	$71.35	$71.30
Purchase #2	$100.31	5.315%	$105.6415	$105.64	$105.65	$105.60
Purchase #3	$49.55	8.294%	$53.6597	$53.66	$53.65	$53.70
Purchase #4	$78.63	10.591%	$86.9577	$86.96	$86.95	$87.00
Purchase #5	$109.88	7.493%	$118.1133	$118.11	$118.10	$118.10
Purchase #6	$245.90	9.140%	$268.3753	$268.38	$268.40	$268.40
Purchase #7	$137.99	8.710%	$150.0089	$150.01	$150.00	$150.00
7 purchase totals =	$785.54		$854.1052	$854.11	$854.10	$854.10