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	$59.84	3.358%	$61.8494	$61.85	$61.85	$61.80
Purchase #2	$121.50	6.112%	$128.9261	$128.93	$128.95	$128.90
Purchase #3	$164.55	6.258%	$174.8475	$174.85	$174.85	$174.80
Purchase #4	$58.54	10.864%	$64.8998	$64.90	$64.90	$64.90
Purchase #5	$249.48	12.279%	$280.1136	$280.11	$280.10	$280.10
Purchase #6	$26.56	4.134%	$27.658	$27.66	$27.65	$27.70
Purchase #7	$97.31	7.337%	$104.4496	$104.45	$104.45	$104.40
7 purchase totals =	$777.78		$842.7440	$842.75	$842.75	$842.60