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	$240.58	12.459%	$270.5539	$270.55	$270.55	$270.60
Purchase #2	$80.35	11.380%	$89.4938	$89.49	$89.50	$89.50
Purchase #3	$47.62	12.238%	$53.4477	$53.45	$53.45	$53.40
Purchase #4	$217.95	12.556%	$245.3158	$245.32	$245.30	$245.30
Purchase #5	$214.63	5.620%	$226.6922	$226.69	$226.70	$226.70
Purchase #6	$89.26	13.356%	$101.1816	$101.18	$101.20	$101.20
Purchase #7	$92.74	13.526%	$105.284	$105.28	$105.30	$105.30
7 purchase totals =	$983.13		$1,091.9690	$1,091.96	$1,092.00	$1,092.00