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	$24.99	8.402%	$27.0897	$27.09	$27.10	$27.10
Purchase #2	$79.77	6.117%	$84.6495	$84.65	$84.65	$84.60
Purchase #3	$86.75	4.399%	$90.5661	$90.57	$90.55	$90.60
Purchase #4	$82.66	8.473%	$89.6638	$89.66	$89.65	$89.70
Purchase #5	$152.28	12.540%	$171.3759	$171.38	$171.40	$171.40
Purchase #6	$106.45	7.319%	$114.2411	$114.24	$114.25	$114.20
Purchase #7	$102.56	13.634%	$116.543	$116.54	$116.55	$116.50
7 purchase totals =	$635.46		$694.1291	$694.13	$694.15	$694.10