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	$81.41	10.403%	$89.8791	$89.88	$89.90	$89.90
Purchase #2	$34.94	12.609%	$39.3456	$39.35	$39.35	$39.30
Purchase #3	$81.53	5.685%	$86.165	$86.17	$86.15	$86.20
Purchase #4	$250.46	11.873%	$280.1971	$280.20	$280.20	$280.20
Purchase #5	$98.61	6.134%	$104.6587	$104.66	$104.65	$104.70
Purchase #6	$169.77	12.448%	$190.903	$190.90	$190.90	$190.90
Purchase #7	$124.76	13.225%	$141.2595	$141.26	$141.25	$141.30
7 purchase totals =	$841.48		$932.4080	$932.42	$932.40	$932.50