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	$180.60	8.849%	$196.5813	$196.58	$196.60	$196.60
Purchase #2	$142.33	4.264%	$148.399	$148.40	$148.40	$148.40
Purchase #3	$81.60	10.560%	$90.217	$90.22	$90.20	$90.20
Purchase #4	$26.30	4.494%	$27.4819	$27.48	$27.50	$27.50
Purchase #5	$7.56	4.457%	$7.8969	$7.90	$7.90	$7.90
Purchase #6	$105.85	8.511%	$114.8589	$114.86	$114.85	$114.90
Purchase #7	$44.71	10.410%	$49.3643	$49.36	$49.35	$49.40
7 purchase totals =	$588.95		$634.7993	$634.80	$634.80	$634.90