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	$206.51	9.214%	$225.5378	$225.54	$225.55	$225.50
Purchase #2	$82.93	8.196%	$89.7269	$89.73	$89.75	$89.70
Purchase #3	$125.79	6.794%	$134.3362	$134.34	$134.35	$134.30
Purchase #4	$58.39	10.181%	$64.3347	$64.33	$64.35	$64.30
Purchase #5	$98.59	10.867%	$109.3038	$109.30	$109.30	$109.30
Purchase #6	$170.28	12.287%	$191.2023	$191.20	$191.20	$191.20
Purchase #7	$29.56	13.602%	$33.5808	$33.58	$33.60	$33.60
7 purchase totals =	$772.05		$848.0225	$848.02	$848.10	$847.90